#include <bits/stdc++.h>
using namespace std;
int main() {
  int N, M;
  cin >> N >> M;
  int s[M], c[M], j, b = 1, a, A = 0, B = 0, C = 0, D = 0;
  if (M == 0) {
    for (int i = 0; i < (int)N - 1; i++) {
      b *= 10;
      A = b;
    }
    cout << A << endl;
    D++;
  } else {
    for (int i = 0; i < (int)M; i++) {
      j = i;
      cin >> s[i] >> c[i];
      if (s[i] == 1 && c[i] == 0 && N != 1) {
        cout << -1 << endl;
        D++;
        break;
      }
      while (j > 0) {
        j--;
        if (s[i] == s[j] && c[i] != c[j]) {
          cout << -1 << endl;
          D++;
          break;
        }
        for (int d = 0; d < (int)N - s[i]; d++) {
          b *= 10;
        }
        if (s[i] == 1) {
          A = c[i] * b;
        }
        if (s[i] == 2) {
          B = c[i] * b;
        }
        if (s[i] == 3) {
          C = c[i] * b;
        }
        b = 1;
      }
    }
  }
  a = (A + B + C);
  if (D == 0) {
    cout << a << endl;
  }
  return 0;
}
