#include <bits/stdc++.h>
using namespace std;
int main() {
  string buf = "000";
  long long n, m;
  bool flag = true;
  cin >> n >> m;
  vector<vector<long long>> s(m, vector<long long>(2));
  for (long long i = 0; i < m; i++) cin >> s[i][0] >> s[i][1];
  sort(s.begin(), s.end());
  if (s.size() == 1) {
    if (s[0][0] == 1 && s[0][1] == 0) flag = false;
  } else {
    for (long long i = 0; i < s.size() - 1; i++) {
      if (s[i][0] == s[i + 1][0] && s[i][1] == s[i + 1][1])
        continue;
      else if ((s[i][0] == s[i + 1][0]) || (s[i][0] == 1 && s[i][1] == 0))
        flag = false;
    }
  }
  if (flag) {
    for (long long i = 0; i < s.size(); i++) {
      buf[s[i][0] - 1] = s[i][1] + '0';
    }
    char ans[3];
    for (long long i = 0; i < n; i++) ans[i] = buf[i];
    cout << atoi(ans) << endl;
  } else
    cout << "-1" << endl;
}
