#include <bits/stdc++.h>
int main() {
  int num[4] = {0, -1, -1, -1};
  int N, M;
  scanf("%d %d", &N, &M);
  int s[5], c[5];
  for (int i = 1; i <= M; i++) {
    scanf("%d %d", &s[i], &c[i]);
    if (num[s[i]] == -1 || num[s[i]] == c[i])
      num[s[i]] = c[i];
    else {
      printf("-1");
      return 0;
    }
  }
  if (num[1] == 0) {
    if (N > 1) printf("-1");
    return 0;
  }
  if (num[1] == -1) {
    if (N > 1) num[1] = 1;
  }
  for (int i = 1; i <= N; i++) {
    if (num[i] == -1) num[i] = 0;
    printf("%d", num[i]);
  }
  return 0;
}
