#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m;
  cin >> n >> m;
  char c[n];
  for (int j = 0; j < n; j++) {
    c[j] = '!';
  }
  int a[m][2], flag = 0;
  for (int i = 0; i < m; i++) {
    scanf("%d %d", &a[i][0], &a[i][1]);
  }
  for (int p = 0; p < m; p++) {
    if (((c[a[p][0] - 1]) == '!') || ((c[a[p][0] - 1]) == '0' + a[p][1]))
      c[a[p][0] - 1] = '0' + a[p][1];
    else if (c[a[p][0] - 1] != '0' + a[p][1]) {
      flag = 1;
      break;
    }
  }
  if (c[0] == '0')
    flag = 1;
  else if (c[0] == '!')
    c[0] = '1';
  if (flag)
    cout << "-1" << endl;
  else {
    for (int x = 0; x < n; x++) {
      if (c[x] == '!')
        cout << "0";
      else
        cout << c[x];
    }
  }
}
