#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using vi = vector<int>;
using vs = vector<string>;
int exponential(int a, int b) {
  int sum = 1;
  if (b != 0) {
    for (int i = 0; i < b; i++) {
      sum *= a;
    }
  }
  return sum;
}
int main() {
  int n, m;
  cin >> n >> m;
  if (m == 0) {
    if (n == 1)
      cout << 0 << endl;
    else
      cout << pow(10, n - 1) << endl;
  } else {
    vi s(m);
    vector<char> c(m);
    for (int i = 0; i < m; i++) cin >> s[i] >> c[i];
    int n0 = exponential(10, n - 1);
    int nend = exponential(10, n);
    int ans = -1;
    for (int i = n0; i < nend; i++) {
      bool issc = true;
      string str = to_string(i);
      for (int j = 0; j < m; j++) {
        if (str[s[j] - 1] != c[j]) {
          issc = false;
        }
      }
      if (issc) {
        ans = i;
        break;
      }
    }
    cout << ans << endl;
  }
}
