#include <bits/stdc++.h>
using namespace std;
int main() {
  int a = -2, b = -2, c = -2;
  int n, m;
  cin >> n;
  cin >> m;
  for (int i = 0; i < m; i++) {
    int d, e;
    cin >> d;
    cin >> e;
    switch (d) {
      case 1:
        if (a != -2) {
          a = e;
        } else {
          if (a != e) {
            std::cout << "-1" << endl;
            return 0;
          }
        }
        break;
      case 2:
        if (b != -2) {
          b = e;
        } else {
          if (b != e) {
            std::cout << "-1" << endl;
            return 0;
          }
        }
        break;
      case 3:
        if (c != -2) {
          c = e;
        } else {
          if (c != e) {
            std::cout << "-1" << endl;
            return 0;
          }
        }
        break;
      default:
        break;
    }
  }
  if (a == -2) {
    a = 0;
  }
  if (b == -2) {
    b = 0;
  }
  if (c == -2) {
    c = 0;
  }
  int ret = 0;
  ret += (a * 100);
  ret += (b * 10);
  ret += c;
  if (to_string(ret).length() != n) {
    cout << "-1" << endl;
  } else {
    cout << ret << endl;
  }
  return 0;
}
