#include <bits/stdc++.h>
using namespace std;
long long int gcd(long long int a, long long int b) {
  return b == 0 ? a : gcd(b, a % b);
}
long long int power(long long int x, long long int n) {
  long long int result = 1;
  while (n > 0) {
    if (n % 2 == 1) result = (result * x) % 1000000007;
    x = (x * x) % 1000000007;
    n = n / 2;
  }
  return result % 1000000007;
}
bool isPrime(long long int n) {
  if (n <= 1) return false;
  if (n <= 3) return true;
  if (n % 2 == 0 || n % 3 == 0) return false;
  for (long long int i = 5; i * i <= n; i = i + 6)
    if (n % i == 0 || n % (i + 2) == 0) return false;
  return true;
}
long long int c[4];
signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  long long int n, m;
  cin >> n >> m;
  bool a[5];
  memset(a, false, sizeof(a));
  long long int s = 1;
  for (long long int i = 0; i < m; i++) {
    long long int x, y;
    cin >> x >> y;
    if (a[x] != false && c[x] != y)
      s = 0;
    else {
      c[x] = y;
      a[x] = true;
    }
  }
  if (c[1] == 0 && n > 1) s = 0;
  if (s == 0)
    cout << -1;
  else {
    for (long long int i = 1; i <= n; i++) {
      if (a[i] == false) {
        if (i == 1 && n != 1)
          cout << 1;
        else
          cout << 0;
      } else
        cout << c[i];
    }
  }
}
