#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m;
  cin >> n >> m;
  int a[n];
  for (int i = 0; i < n; i++) {
    a[i] = -1;
  }
  for (int i = 0; i < m; i++) {
    int s, c;
    cin >> s >> c;
    if (a[s - 1] == -1 || a[s - 1] == c) {
      a[s - 1] = c;
    } else {
      cout << "-1" << endl;
      return 0;
    }
  }
  if (a[0] == 0 && n > 1) {
    cout << "-1" << endl;
  } else if (a[0] == 0 && n == 1) {
    cout << "0" << endl;
  } else {
    if (a[0] == -1 && n > 1) {
      a[0] = 1;
    } else if (a[0] == -1 && n == 1) {
      a[0] = 0;
    }
  }
  for (int i = 0; i < n; i++) {
    if (a[i] == -1) {
      cout << "0";
    } else {
      cout << a[i];
    }
  }
  return 0;
}
