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
from __future__ import print_function
[N, M] = map(int, raw_input().split())
d = [-1 for i in range(N)]
for i in range(M):
    [a,b] = map(int, raw_input().split())
    if d[a-1] == -1:
        d[a-1] = b
    elif d[a-1] != b:
        print("-1")
        exit(0)

if N == 1 and M == 0:
    print (0)
    exit(0)

if d[0] == -1:
    #print 1,
    print("1",end="")
elif d[0] == 0 and N > 1:
    print ("-1")
    exit(0)
elif N > 1:
    #print d[0],
    print(d[0], end="")

for i in range(1,N-1):
        if d[i] == -1:
            #print 0,
            print("0",end="")
        else:
            #print d[i],
            print(d[i], end="")

if d[N-1] == -1:
    #print 0
    print(0)
else:
    #print d[N-1]
    print(d[N-1])
