#!/usr/bin/env python3
import sys


def solve(N: int, M: int, s: "List[int]", c: "List[int]"):
    for i in range(pow(10,N-1),pow(10,N)):
        f=True
        for j in range(M):
            if not(str(i)[s[j]-1]==str(c[j])):f=False
            if(not f):break
        if(f):
            print(i)
            return
    print(-1)
    return


# Generated by 1.1.6 https://github.com/kyuridenamida/atcoder-tools  (tips: You use the default template now. You can remove this line by using your custom template)
def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  # type: int
    M = int(next(tokens))  # type: int
    s = [int()] * (M)  # type: "List[int]"
    c = [int()] * (M)  # type: "List[int]"
    for i in range(M):
        s[i] = int(next(tokens))
        c[i] = int(next(tokens))
    solve(N, M, s, c)

if __name__ == '__main__':
    main()
