#include <bits/stdc++.h>
int main() {
  int N, M, s[6], c[6];
  scanf("%d %d", &N, &M);
  for (int i = 0; i < M; i++) scanf("%d %d", &s[i], &c[i]);
  int p = 1;
  for (int i = 1; i < N; i++) p *= 10;
  for (int d = p; d < p * 10; d++) {
    char S[10];
    sprintf(S, "%d", d);
    int g = 0;
    for (int k = 0; k < M; k++) {
      if (S[s[k] - 1] == c[k] + '0') g++;
    }
    if (g == M) {
      puts(S);
      return 0;
    }
  }
  puts("-1");
  return 0;
}
