#include <bits/stdc++.h>
using namespace std;
int N, M, s[10], c[10];
int main() {
  scanf("%d %d", &N, &M);
  for (int i = 1; i <= M; ++i) scanf("%d %d", &s[i], &c[i]);
  int st = N > 1 ? pow(10, N - 1) : 0, ans = -1;
  for (int i = st; i <= pow(10, N) - 1; ++i) {
    int num[4] = {0, i / 100, (i % 100) / 10, (i % 10) / 1}, cnt = 0;
    for (int j = 1; j <= M; ++j) {
      if (num[s[j]] == c[j]) ++cnt;
    }
    if (cnt != M) continue;
    ans = i;
    break;
  }
  printf("%d\n", ans);
}
