#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using P = pair<int, int>;
const long long MOD = 1000000007;
const long long INF = 1LL << 60;
const int INT_INF = 1000000000;
int dx[4] = {1, 0, -1, 0}, dy[4] = {0, 1, 0, -1};
int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  int N, M;
  cin >> N >> M;
  vector<int> s(M);
  vector<int> c(M);
  for (int i = 0; i < M; i++) {
    cin >> s[i] >> c[i];
  }
  string ans;
  for (int i = 0; i < pow(10, N); i++) {
    bool ok = true;
    string tmp = to_string(i);
    for (int j = 0; j < M; j++) {
      if (tmp[s[j] - 1] != c[j]) ok = false;
      if ((N == 2 or N == 3) && s[j] == 1 && c[j] == '0') {
        break;
      }
    }
    if (ok) {
      cout << ans << endl;
      return 0;
    }
  }
  cout << -1 << endl;
  return 0;
}
