#include <bits/stdc++.h>
using namespace std;
int n, m;
int ans[10];
int main() {
  memset(ans, -1, sizeof(ans));
  scanf("%d%d", &n, &m);
  while (m--) {
    int s, c;
    scanf("%d%d", &s, &c);
    if (ans[s] == -1) {
      ans[s] = c;
    } else if (ans[s] != c) {
      printf("-1\n");
      return 0;
    }
  }
  if (ans[1] == 0 && n > 1) {
    printf("-1\n");
    return 0;
  }
  if (ans[1] == -1) ans[1] = 1;
  for (int i = 1; i <= n; i++) {
    if (ans[i] == -1) ans[i] = 0;
    printf("%d", ans[i]);
  }
  printf("\n");
  return 0;
}
