#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
using namespace std;
int dx[8] = {1, 0, -1, 0, 1, -1, -1, 1};
int dy[8] = {0, 1, 0, -1, 1, 1, -1, -1};
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;
}
struct io {
  io() {
    ios::sync_with_stdio(false);
    cin.tie(0);
  }
};
const int INF = INT_MAX;
const long long int LLINF = 1LL << 60;
const long long int MOD = 1000000007;
const double EPS = 1e-9;
int main(void) {
  int n, m;
  cin >> n >> m;
  vector<int> v(n, -1);
  for (int i = 0; i < (m); ++i) {
    int s, c;
    cin >> s >> c;
    s--;
    if (v[s] == -1 || v[s] == c) {
      v[s] = c;
    } else {
      cout << (-1) << '\n';
      return 0;
    }
  }
  for (int i = 0; i < (n); ++i) {
    if (v[i] == -1) v[i] = 0;
  }
  if (v[0] == 0) {
    cout << (-1) << '\n';
    return 0;
  }
  for (int i = 0; i < (n); ++i) cout << v[i];
  cout << endl;
}
