#!/usr/bin/env python3
import sys


def solve(N: int, M: int, s: "List[int]", c: "List[int]"):
    ans = ["1"] + ["0" for _ in range(N - 1)]

    modified = [False for _ in range(N)]

    for i in range(M):
        keta = s[i] - 1
        if modified[keta] and ans[keta] != str(c[i]):
            print(-1)
            return
        if s[i] > N:
            print(-1)
            return
        modified[keta] = True
        ans[keta] = str(c[i])

    if N > 1 and ans[0] == "0":
        print(-1)
        return

    print("".join(ans))
    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()
