#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  long long int n, m, i, x, y;
  string str;
  cin >> n >> m;
  for (i = 0; i < n; i++) str += '0';
  for (i = 0; i < m; i++) {
    cin >> x >> y;
    str[x - 1] = char(y + 48);
  }
  if (str[0] == '0') {
    if (m == 0) {
      for (i = 0; i < n; i++) {
        if (i == 0)
          cout << "1";
        else
          cout << '0';
      }
      cout << endl;
    } else {
      if (n == 1)
        cout << str << endl;
      else
        cout << "-1" << endl;
    }
  } else
    cout << str << endl;
  return 0;
}
