#include <bits/stdc++.h>
using namespace std;
template <class T>
inline bool chmax(T& a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T>
inline bool chmin(T& a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
using Graph = vector<vector<long long>>;
struct edge {
  long long from, to, cost;
};
signed main() {
  long long a, b;
  cin >> a >> b;
  vector<long long> c(b), d(b);
  for (long long i = 0; i < b; i++) cin >> c[i] >> d[i];
  bool ans = 0;
  vector<long long> e(a);
  for (long long i = 0; i < a; i++) e[i] = -1;
  for (long long i = 0; i < b; i++) {
    if (c[i] == 1 && d[i] == 0)
      ans = 1;
    else if (e[c[i] - 1] != -1 && e[c[i] - 1] != d[i])
      ans = 1;
    else
      e[c[i] - 1] = d[i];
  }
  if (ans)
    cout << -1;
  else {
    for (long long i = 0; i < a; i++) {
      if (i == 0) {
        if (e[i] == -1)
          cout << 1;
        else
          cout << e[i];
      } else {
        if (e[i] != -1)
          cout << e[i];
        else
          cout << 0;
      }
    }
  }
}
