If there is an integer not less than 0 satisfying the following conditions, print the smallest such integer; otherwise, print `-1`.

* The integer has exactly N digits in base ten. (We assume 0 to be a 1-digit integer. For other integers, leading zeros are not allowed.)
* The s_i-th digit from the left is c_i. \left(i = 1, 2, \cdots, M\right)

Constraints

* All values in input are integers.
* 1 \leq N \leq 3
* 0 \leq M \leq 5
* 1 \leq s_i \leq N
* 0 \leq c_i \leq 9

Input

Input is given from Standard Input in the following format:


N M
s_1 c_1
\vdots
s_M c_M


Output

Print the answer.

Examples

Input

3 3
1 7
3 2
1 7


Output

702


Input

3 2
2 1
2 3


Output

-1


Input

3 1
1 0


Output

-1
import sys
N,M=map(int, sys.stdin.readline().split())
SC=[ map(int, sys.stdin.readline().split()) for _ in range(M) ]

def judge(s,c,n):
    n=str(n)
    c=str(c)
    l=len(n)
    if l<s: return False
    if l!=N:return False
    if n[s-1]==c:
        return True
    else:
        return False

if M==0:
    if N==3: print 100
    elif N==2: print 10
    elif N==1: print 0
    quit()

for n in range(1000):
    for s,c in SC:
        if not judge(s,c,n):
            break
    else:
        print n
        quit()
else:
    print -1