#!/usr/bin/env python3
import sys


def solve(N: int, M: int, s: "List[int]", c: "List[int]"):
    answer = 'x' * N
    s = [x-1 for x in s]
    for i in range(M):
        if list(answer)[s[i]] == 'x':
            answer = answer[:s[i]] + str(c[i]) + answer[s[i]+1:]
        else:
            if str(c[i]) != answer[s[i]]:
                print(-1)
                return
    answer = ''.join(answer)
    answer = answer.replace('x', '0')
    answer = int(answer)
    answer = str(answer)
    if len(answer) == N:
        print(answer)
    else:
        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()
