#include <bits/stdc++.h>
using namespace std;
int main() {
  int N, M;
  cin >> N >> M;
  vector<vector<int>> K(M, vector<int>(2));
  for (int i = 0; i < M; i++) {
    for (int j = 0; j < 2; j++) {
      cin >> K.at(i).at(j);
    }
  }
  if (N != 1) {
    int a = 0;
    bool finished = false;
    for (int i = 0; i < M; i++) {
      for (int j = i; j < M; j++) {
        if (K.at(i).at(0) == K.at(j).at(0) && K.at(i).at(1) != K.at(j).at(1)) {
          a = -1;
          cout << a << endl;
          finished = true;
          break;
        }
      }
      if (finished) {
        break;
      }
    }
    if (a == 0) {
      for (int i = 0; i < M; i++) {
        if (K.at(i).at(0) == 1 && K.at(i).at(1) == 0) {
          a = -1;
          cout << a << endl;
          break;
        }
      }
    }
    if (a == 0) {
      vector<int> A(N);
      A.at(0) = 1;
      for (int i = 1; i < N; i++) {
        A.at(i) = 0;
      }
      for (int i = 0; i < N; i++) {
        for (int j = 0; j < M; j++) {
          if (i + 1 == K.at(j).at(0)) {
            A.at(i) = K.at(j).at(1);
          }
        }
      }
      for (int i = 0; i < N; i++) {
        cout << A.at(i);
      }
    }
  } else {
    cout << K.at(0).at(1);
  }
}
