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