Note that the only difference between String Transformation 1 and String Transformation 2 is in the move Koa does. In this version the letter y Koa selects must be strictly greater alphabetically than x (read statement for better understanding). You can make hacks in these problems independently.

Koa the Koala has two strings A and B of the same length n (|A|=|B|=n) consisting of the first 20 lowercase English alphabet letters (ie. from a to t).

In one move Koa:

  1. selects some subset of positions p_1, p_2, …, p_k (k ≥ 1; 1 ≤ p_i ≤ n; p_i ≠ p_j if i ≠ j) of A such that A_{p_1} = A_{p_2} = … = A_{p_k} = x (ie. all letters on this positions are equal to some letter x).

  2. selects a letter y (from the first 20 lowercase letters in English alphabet) such that y>x (ie. letter y is strictly greater alphabetically than x).

  3. sets each letter in positions p_1, p_2, …, p_k to letter y. More formally: for each i (1 ≤ i ≤ k) Koa sets A_{p_i} = y.

Note that you can only modify letters in string A.




Koa wants to know the smallest number of moves she has to do to make strings equal to each other (A = B) or to determine that there is no way to make them equal. Help her!

Input

Each test contains multiple test cases. The first line contains t (1 ≤ t ≤ 10) — the number of test cases. Description of the test cases follows.

The first line of each test case contains one integer n (1 ≤ n ≤ 10^5) — the length of strings A and B.

The second line of each test case contains string A (|A|=n).

The third line of each test case contains string B (|B|=n).

Both strings consists of the first 20 lowercase English alphabet letters (ie. from a to t).

It is guaranteed that the sum of n over all test cases does not exceed 10^5.

Output

For each test case:

Print on a single line the smallest number of moves she has to do to make strings equal to each other (A = B) or -1 if there is no way to make them equal.

Example

Input


5
3
aab
bcc
4
cabc
abcb
3
abc
tsr
4
aabd
cccd
5
abcbd
bcdda


Output


2
-1
3
2
-1

Note

  * In the 1-st test case Koa: 
    1. selects positions 1 and 2 and sets A_1 = A_2 =  b (\color{red}{aa}b → \color{blue}{bb}b). 
    2. selects positions 2 and 3 and sets A_2 = A_3 =  c (b\color{red}{bb} → b\color{blue}{cc}). 

  * In the 2-nd test case Koa has no way to make string A equal B.

  * In the 3-rd test case Koa: 
    1. selects position 1 and sets A_1 =  t (\color{red}{a}bc → \color{blue}{t}bc). 
    2. selects position 2 and sets A_2 =  s (t\color{red}{b}c → t\color{blue}{s}c). 
    3. selects position 3 and sets A_3 =  r (ts\color{red}{c} → ts\color{blue}{r}). 
from sys import stdin
from collections import deque
# https://codeforces.com/contest/1354/status/D
mod = 10**9 + 7
import sys
import random
# sys.setrecursionlimit(10**6)
from queue import PriorityQueue
from collections import Counter as cc
# def rl():
#     return [int(w) for w in stdin.readline().split()]
from bisect import bisect_right
from bisect import bisect_left
from collections import defaultdict
from math import sqrt,factorial,gcd,log2,inf,ceil
# map(int,input().split())
# # l = list(map(int,input().split()))
# from itertools import permutations
import heapq
# input = lambda: sys.stdin.readline().rstrip()
input = lambda : sys.stdin.readline().rstrip()
from sys import stdin, stdout
from heapq import heapify, heappush, heappop
from itertools import permutations
from math import factorial as f

# def ncr(x, y):
#     return f(x) // (f(y) * f(x - y))
def ncr(n, r, p):
    num = den = 1
    for i in range(r):
        num = (num * (n - i)) % p
        den = (den * (i + 1)) % p
    return (num * pow(den,
                      p - 2, p)) % p

import sys

# input = sys.stdin.readline
# LCA
# def bfs(na):
#
#     queue = [na]
#     boo[na] = True
#     level[na] = 0
#
#     while queue!=[]:
#
#         z = queue.pop(0)
#
#         for i in hash[z]:
#
#             if not boo[i]:
#
#                 queue.append(i)
#                 level[i] = level[z] + 1
#                 boo[i] = True
#                 dp[i][0] = z
#
#
#
# def prec(n):
#
#     for i in range(1,20):
#
#         for j in range(1,n+1):
#             if dp[j][i-1]!=-1:
#                 dp[j][i] = dp[dp[j][i-1]][i-1]
#
#
# def lca(u,v):
#     if level[v] < level[u]:
#         u,v = v,u
#
#     diff = level[v] - level[u]
#
#
#     for i in range(20):
#         if ((diff>>i)&1):
#             v = dp[v][i]
#
#
#     if u == v:
#         return u
#
#
#     for i in range(19,-1,-1):
#         # print(i)
#         if dp[u][i] != dp[v][i]:
#
#             u = dp[u][i]
#             v = dp[v][i]
#
#
#     return dp[u][0]
#
# dp = []
#
#
# n = int(input())
#
# for i in range(n + 10):
#
#     ka = [-1]*(20)
#     dp.append(ka)


# class FenwickTree:
#     def __init__(self, x):
#         """transform list into BIT"""
#         self.bit = x
#         for i in range(len(x)):
#             j = i | (i + 1)
#             if j < len(x):
#                 x[j] += x[i]
#
#     def update(self, idx, x):
#         """updates bit[idx] += x"""
#         while idx < len(self.bit):
#             self.bit[idx] += x
#             idx |= idx + 1
#
#     def query(self, end):
#         """calc sum(bit[:end])"""
#         x = 0
#         while end:
#             x += self.bit[end - 1]
#             end &= end - 1
#         return x
#
#     def find_kth_smallest(self, k):
#         """Find largest idx such that sum(bit[:idx]) <= k"""
#         idx = -1
#         for d in reversed(range(len(self.bit).bit_length())):
#             right_idx = idx + (1 << d)
#             if right_idx < len(self.bit) and k >= self.bit[right_idx]:
#                 idx = right_idx
#                 k -= self.bit[idx]
#         return idx + 1



# import sys
# def rs(): return sys.stdin.readline().strip()
# def ri(): return int(sys.stdin.readline())
# def ria(): return list(map(int, sys.stdin.readline().split()))
# def prn(n): sys.stdout.write(str(n))
# def pia(a): sys.stdout.write(' '.join([str(s) for s in a]))
#
#
# import gc, os
#
# ii = 0
# _inp = b''
#
#
# def getchar():
#     global ii, _inp
#     if ii >= len(_inp):
#         _inp = os.read(0, 100000)
#         gc.collect()
#         ii = 0
#     if not _inp:
#         return b' '[0]
#     ii += 1
#     return _inp[ii - 1]
#
#
# def input():
#     c = getchar()
#     if c == b'-'[0]:
#         x = 0
#         sign = 1
#     else:
#         x = c - b'0'[0]
#         sign = 0
#     c = getchar()
#     while c >= b'0'[0]:
#         x = 10 * x + c - b'0'[0]
#         c = getchar()
#     if c == b'\r'[0]:
#         getchar()
#     return -x if sign else x

# fenwick Tree

# n,q = map(int,input().split())
#
#
# l1 = list(map(int,input().split()))
#
# l2 = list(map(int,input().split()))
#
# bit = [0]*(10**6 + 1)
#
# def update(i,add,bit):
#
#     while i>0 and i<len(bit):
#
#         bit[i]+=add
#         i = i + (i&(-i))
#
#
# def sum(i,bit):
#     ans = 0
#     while i>0:
#
#         ans+=bit[i]
#         i = i - (i & ( -i))
#
#
#     return ans
#
# def find_smallest(k,bit):
#
#     l = 0
#     h = len(bit)
#     while l<h:
#
#         mid = (l+h)//2
#         if k <= sum(mid,bit):
#             h = mid
#         else:
#             l = mid + 1
#
#
#     return l
#
#
# def insert(x,bit):
#     update(x,1,bit)
#
# def delete(x,bit):
#     update(x,-1,bit)
# fa = set()
#
# for i in l1:
#     insert(i,bit)
#
#
# for i in l2:
#     if i>0:
#         insert(i,bit)
#
#     else:
#         z = find_smallest(-i,bit)
#
#         delete(z,bit)
#
#
# # print(bit)
# if len(set(bit)) == 1:
#     print(0)
# else:
#     for i in range(1,n+1):
#         z = find_smallest(i,bit)
#         if z!=0:
#             print(z)
#             break
#

# service time problem


# def solve2(s,a,b,hash,z,cnt):
#     temp = cnt.copy()
#     x,y = hash[a],hash[b]
#     i = 0
#     j = len(s)-1
#
#     while z:
#
#         if s[j] - y>=x-s[i]:
#             if temp[s[j]]-1 == 0:
#                 j-=1
#             temp[s[j]]-=1
#             z-=1
#
#
#         else:
#             if temp[s[i]]-1 == 0:
#                 i+=1
#
#             temp[s[i]]-=1
#             z-=1
#
#     return s[i:j+1]
#
#
#
#
#
# def solve1(l,s,posn,z,hash):
#
#     ans = []
#     for i in l:
#         a,b = i
#         ka = solve2(s,a,b,posn,z,hash)
#         ans.append(ka)
#
#         return ans
#
# def consistent(input, window, min_entries, max_entries, tolerance):
#
#     l = input
#     n = len(l)
#     l.sort()
#     s = list(set(l))
#     s.sort()
#
#     if min_entries<=n<=max_entries:
#
#         if s[-1] - s[0]<window:
#             return True
#         hash = defaultdict(int)
#         posn = defaultdict(int)
#         for i in l:
#             hash[i]+=1
#
#         z = (tolerance*(n))//100
#         poss_window = set()
#
#
#         for i in range(len(s)):
#                 posn[i] = l[i]
#                 for j in range(i+1,len(s)):
#                     if s[j]-s[i] == window:
#                         poss_window.add((s[i],s[j]))
#
#         if poss_window!=set():
#             print(poss_window)
#             ans = solve1(poss_window,s,posn,z,hash)
#             print(ans)
#
#
#         else:
#             pass
#
#     else:
#         return False
#
#
#
#
# l = list(map(int,input().split()))
#
# min_ent,max_ent = map(int,input().split())
# w = int(input())
# tol = int(input())
# consistent(l, w, min_ent, max_ent, tol)

# t = int(input())
#
# for i in range(t):
#
#     n,x = map(int,input().split())
#
#     l = list(map(int,input().split()))
#
#     e,o = 0,0
#
#     for i in l:
#         if i%2 == 0:
#             e+=1
#         else:
#             o+=1
#
#     if e+o>=x and o!=0:
#         z = e+o - x
#         if z == 0:
#             if o%2 == 0:
#                 print('No')
#             else:
#                 print('Yes')
#             continue
#         if o%2 == 0:
#             o-=1
#             z-=1
#             if e>=z:
#                 print('Yes')
#             else:
#                 z-=e
#                 o-=z
#                 if o%2!=0:
#                     print('Yes')
#                 else:
#                     print('No')
#
#         else:
#
#             if e>=z:
#                 print('Yes')
#             else:
#                 z-=e
#                 o-=z
#                 if o%2!=0:
#                     print('Yes')
#                 else:
#                     print('No')
#     else:
#         print('No')
#
#
#
#
#
#
#
# def dfs(n):
#     boo[n] = True
#     dp2[n] = 1
#     for i in hash[n]:
#         if not boo[i]:
#
#             dfs(i)
#             dp2[n] += dp2[i]




































#
#
# n = int(input())
# x = 0
# l = list(map(int,input().split()))
# for i in range(n):
#
#      x = l[i]|x
#
# z = list(bin(x)[2:])
# ha = z.copy()
# k = z.count('1')
# ans = 0
# # print(z)
# cnt = 0
# for i in range(20):
#
#
#         maxi = 0
#         idx = -1
#
#         for j in range(n):
#             k = bin(l[j])[2:]
#             k = '0'*(len(z) -len(k)) + k
#             cnt = 0
#             for i in range(len(z)):
#                 if k[i] == z[i] == '1':
#                     cnt+=1
#
#             maxi = max(maxi,cnt)
#             if maxi == cnt:
#                 idx = j
#         if idx!=-1:
#
#             k = bin(l[idx])[2:]
#             k = '0'*(len(z) -len(k)) + k
#
#             for i in range(len(z)):
#                 if k[i] == z[i] == '1':
#                     z[i] = '0'
#             l[idx] = 0
#
#
# ans = 0
# for i in range(len(z)):
#     if z[i] == '0' and ha[i] == '1':
#         ans+=1
# flip = 0
# for i in range(ans):
#     flip+=2**i
#
#
#
# print(flip)

# def search(k,l,low):
#
#     high = len(l)-1
#     z = bisect_left(l,k,low,high)
#
#     return z
#
#
#
#
#
#
# n,x = map(int,input().split())
#
# l = list(map(int,input().split()))
#
# prefix = [0]
# ha = [0]
# for i in l:
#     prefix.append(i + prefix[-1])
#     ha.append((i*(i+1))//2 + ha[-1])
# fin = 0
# print(prefix)
# for i in range(n):
#     ans = 0
#     if l[i]<x:
#
#
#         if prefix[-1]-prefix[i]>=x:
#
#             z = search(x+prefix[i],prefix,i+1)
#             print(z)
#             z+=i+1
#             k1 = x-(prefix[z-1]-prefix[i])
#             ans+=ha[z-1]
#             ans+=(k1*(k1+1))//2
#
#
#         else:
#             z1 = x - (prefix[-1]-prefix[i])
#             z = search(z1,prefix,1)
#
#             k1 = x-prefix[z-1]
#             ans+=ha[z-1]
#             ans+=(k1*(k1+1))//2
#
#
#
#
#     elif l[i]>x:
#         z1 = ((l[i])*(l[i]+1))//2
#         z2 = ((l[i]-x)*(l[i]-x+1))//2
#         ans+=z1-z2
#     else:
#         ans+=(x*(x+1))//2





# t = int(input())
#
# for _ in range(t):
#
#     s = list(input())
#     ans = [s[0]]
#
#     for i in range(1,len(s)-1,2):
#         ans.append(s[i])
#
#     ans.append(s[-1])
#     print(''.join(ans))
#
#
#
# t = int(input())
#
# for _ in range(t):
#
#     n = int(input())
#     l = list(map(int,input().split()))
#     ans = 0
#     for i in range(n):
#         if l[i]%2!=i%2:
#             ans+=1
#
#     if ans%2 == 0:
#         print(ans//2)
#     else:
#        print(-1)


# t = int(input())
#
# for _ in range(t):
#
#     n,k = map(int,input().split())
#     s = input()
#
#
#     ans = 0
#     ba = []
#     for i in range(n):
#         if s[i] == '1':
#             ba.append(i)
#     if ba == []:
#         for i in range(0,n,k+1):
#             ans+=1
#
#         print(ans)
#         continue
#
#     i = s.index('1')
#     c = 0
#     for x in range(i-1,-1,-1):
#         if c == k:
#             c = 0
#             ans+=1
#         else:
#             c+=1
#
#
#     while i<len(s):
#         count = 0
#         dis = 0
#         while s[i] == '0':
#             dis+=1
#             if dis == k:
#                 dis = 0
#                 count+=1
#             if dis<k and s[i] == '1':
#                 count-=1
#                 break
#             i+=1
#             if i == n:
#                 break
#         i+=1
#
#     print(ans)
#
#
#
#

# q1

# def poss1(x):
#     cnt = 1
#     mini = inf
#     for i in l:
#         if cnt%2 != 0:
#           cnt+=1
#         else:
#             if i<=x:
#                 cnt+=1
#                 mini = min()
#         if cnt  == k:
#             return
#
#     return -1
#
#
#
#
# def poss2(x):
#     cnt = 1
#     for i in l:
#         if cnt%2 == 0:
#             cnt+=1
#         else:
#             if i<=x:
#                 cnt+=1
#         if cnt  == k:
#             return
#
#     return -1
#
#
#
# n,k = map(int,input().split())
# l = list(map(int,input().split()))
#
# z1 = min(l)
# z2 = max(l)







# t = int(input())
#
# for _ in range(t):
#
#     n,k = map(int,input().split())
#     l = list(map(int,input().split()))
#
#     for i in range(n):
#         z = l[i]%k
#
#         if z!=0:
#
#             l[i] = k-z
#         else:
#             l[i] = 0
#
#     l.sort()
#     count = 0
#     ans = 0
#     x = 0
#     print(l)
#     for i in range(n):
#
#             z = l[i]
#             if z == 0:
#                 continue
#             if x>z:
#                 z2 = ceil((x-l[i])/k)
#                 z1 = l[i] + k*z2
#                 # print(x,z1)
#                 ans += z1-x + 1
#                 x = z1+1
#             elif z == x:
#                 ans+=1
#                 x+=1
#             else:
#
#                 ans += z-x + 1
#                 x = z+1
#             # print(i,x)
#             print(ans)
#
#
#
#     print(ans)


# t = int(input())
#
# for _ in range(t):
#
#     n = int(input())
#     seti = set()
#     ans = []
#     for i in range(1,1001):
#         if i not in seti:

# def dfs_cycle(u, p, color,
#               mark, par):
#     global cyclenumber
#
#     # already (completely) visited vertex.
#     if color[u] == 2:
#         return
#
#     # seen vertex, but was not
#     # completely visited -> cycle detected.
#     # backtrack based on parents to
#     # find the complete cycle.
#     if color[u] == 1:
#         cyclenumber += 1
#         cur = p
#         mark[cur] = cyclenumber
#
#         # backtrack the vertex which are
#         # in the current cycle thats found
#         while cur != u:
#             cur = par[cur]
#             mark[cur] = cyclenumber
#
#         return
#
#     par[u] = p
#
#     # partially visited.
#     color[u] = 1
#
#     # simple dfs on graph
#     for v in hash[u]:
#
#         # if it has not been visited previously
#         if v == par[u]:
#             continue
#         dfs_cycle(v, u, color, mark, par)
#
#         # completely visited.
#     color[u] = 2
#
# def printCycles(edges, mark):
#
#     # push the edges that into the
#     # cycle adjacency list
#     for i in range(1, edges + 1):
#         if mark[i] != 0:
#             cycles[mark[i]].append(i)
#
#             # print all the vertex with same cycle
#     for i in range(1, cyclenumber + 1):
#
#         # Print the i-th cycle
#         print("Cycle Number %d:" % i, end = " ")
#         for x in cycles[i]:
#             print(x, end = " ")
#         print()
#
# t = int(input())
#
# for _ in range(t):
#
#     n,m = map(int,input().split())
#
#     hash = defaultdict(list)
#     seti = set()
#     for i in range(m):
#
#         type,a,b = map(int,input().split())
#         hash[a].append(b)
#         hash[b].append(a)
#         if type == 1:
#             seti.add((a,b))
#
#     cycles = defaultdict(list)
#     color = defaultdict(int)
#     par = defaultdict(int)
#     mark = defaultdict(int)
#     cyclenumber = 0
#     dfs_cycle(1, 0, color, mark, par)
#     printCycles(m, mark)
#
#
#
#
#
#



































































































































































    # binary lifting Technique

# n = int(input())
# max_log = int(input())
# dp = []
# for i in range(n+1):
#     c = [0]*(max_log + 1)
#     dp.append(c)
# par = []
# for i in range(1,n+1):
#     for j in range(0,n+1):
#         if (1<<j)>n:
#             break
#         dp[i][j] = -1
#
# for i in range(1,n+1):
#     dp[i][0] = par[i]
#
# for j in range(1,n+1):
#     if (1<<j)>n:
#         break
#     for i in range(1,n+1):
#         if dp[i][j-1]!=-1:
#             dp[i][j] = dp[dp[i][j-1]][j-1]
#
# level = defaultdict(int)
# def lca(u,v):
#  if level[u] < level[v]:
#      u,v = v,u
#
#  dist = level[u] - level[v]
#  while dist>0:
#      raise_by = int(log2(dist))
#      u = dp[u][raise_by]
#      dist-=1<<raise_by
#
#  if u == v:
#      return u
#
#  for j in range(max_log,-1,-1):
#
#      if dp[u][j]!=-1 and dp[u][j]!=dp[v][j]:
#          u = dp[u][j]
#          v = dp[v][j]
#
#
#
#
#
#
#  return par[u]


# n = int(input())

# t = int(input())
#
# for _ in range(t):
#
#     n = int(input())
#     l = list(map(int,input().split()))
#     ans = ['']*(n+1)
#     cnt = 1
#     id = 99
#     for i in range(n-1):
#         a = l[i]
#         s1,s2 = ans[i],ans[i+1]
#         if a == 0:
#
#             ans[i] = chr((id)%97 + 97)*(cnt)
#             if id%97 == 0:
#                 cnt+=1
#             id+=1
#
#         elif s1 == 0:
#             ans[i],ans[i+1] = 'a'*a,'a'*a
#         elif len(s1)<=a:
#             ans[i] = s1 + 'a'*(a-len(s1))
#             ans[i+1] = ans[i]
#         else:
#             ans[i+1] = s1[:a]
#     a = l[-1]
#     s1 = ans[-2]
#
#     if a == 0:
#         ans[-2] =  chr((id+1)%97 + 97)*(cnt)
#         if id%97 == 0:
#             cnt+=1
#         id+=1
#         ans[-1] =  chr((id+1)%97 + 97)*(cnt)
#     elif len(s1)<=a:
#         ans[-2] = s1 + 'a'*(a-len(s1))
#         ans[-1] = ans[-2]
#     else:
#         ans[-1] = s1[:a]
#     for i in ans:
#         print(i)
#
#
#

def find_parent(b):

    while par[b]!=b:

        b = par[b]


    return b

t = int(input())

for _ in range(t):
    n = int(input())

    s1 = input()
    s2 = input()

    if s1 == s2:
        print(0)
        continue
    flag = 0
    for i in range(n):
        if s1[i]>s2[i]:
            flag = 1
            break
    if flag:
        print(-1)
        continue

    par = [i for i in range(30)]
    rank = [1]*(30)

    for i in range(n):
        a,b = ord(s1[i])-97,ord(s2[i])-97

        z1,z2 = find_parent(a),find_parent(b)

        if z1!=z2:
            if rank[z1]>rank[z2]:
                z1,z2 = z2,z1

            par[z1] = z2
            rank[z2]+=rank[z1]

    seti = set()
    for i in s1:
        z = find_parent(ord(i)-97)
        seti.add(z)

    ans = 0
    for i in seti:
        ans+=rank[i]-1

    print(ans)









