#include <bits/stdc++.h>
using namespace std;
const int M = 10;
int nu[M];
int main() {
  int n, m;
  scanf("%d%d", &n, &m);
  int s, c;
  memset(nu, -1, sizeof(nu));
  for (int i = 0; i < m; i++) {
    scanf("%d%d", &s, &c);
    if (nu[s] == -1 || nu[s] == c)
      nu[s] = c;
    else {
      printf("-1\n");
      return 0;
    }
  }
  if (nu[1] == -1) nu[1] = 1;
  if (nu[2] == -1) nu[2] = 0;
  if (nu[3] == -1) nu[3] = 0;
  if (n != 1 && nu[1] == 0) {
    printf("-1\n");
    return 0;
  }
  for (int i = 1; i <= n; i++) printf("%d", nu[i]);
  putchar('\n');
  return 0;
}
