#include <bits/stdc++.h>
const int MGN = 10;
const int ARY_SZ_MAX = (int)1e7;
using namespace std;
using ll = long long;
using ull = unsigned long long;
using vi = vector<int>;
using vvi = vector<vi>;
using vc = vector<char>;
using vvc = vector<vc>;
using vb = vector<bool>;
using vvb = vector<vb>;
using vl = vector<ll>;
using vvl = vector<vl>;
using vd = vector<double>;
using vs = vector<string>;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using psl = pair<string, ll>;
int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  int N, M;
  cin >> N >> M;
  vector<pair<int, char>> SC;
  vi num(N, -1);
  for (int i = int(0); i < int(M); ++i) {
    int S, C;
    cin >> S >> C;
    S--;
    if (num[S] >= 0 && num[S] != C) {
      cout << -1 << endl;
      return 0;
    }
    num[S] = C;
  }
  if (N > 1 && num[0] == 0) {
    cout << -1 << endl;
    return 0;
  }
  string ans = "";
  for (int i = int(0); i < int(N); ++i) {
    if (num[i] < 0)
      ans += i == 0 ? '1' : '0';
    else
      ans += '0' + num[i];
  }
  cout << ans << endl;
  return 0;
}
