#include <bits/stdc++.h>
using namespace std;
template <class T>
bool ckmin(T& a, const T& b) {
  return b < a ? a = b, 1 : 0;
}
template <class T>
bool ckmax(T& a, const T& b) {
  return a < b ? a = b, 1 : 0;
}
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
const long double pii = 3.14159265359;
const int MOD = 1000000007;
const char nl = '\n';
const int MX = 200001;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int N, M;
  cin >> N >> M;
  vector<int> ans(N, -1);
  for (int x = 0; x < (M); x++) {
    int in, val;
    cin >> in >> val;
    in--;
    if (ans[in] != -1 && ans[in] != val) {
      cout << -1;
      return 0;
    }
    ans[in] = val;
  }
  if (N == 1) {
    cout << 0;
    return 0;
  }
  if (ans[0] == 0)
    cout << -1;
  else {
    if (ans[0] == -1) ans[0] = 1;
    cout << ans[0];
    for (int x = 1; x < (N); x++) {
      if (ans[x] == -1) ans[x] = 0;
      cout << ans[x];
    }
  }
  return 0;
}
