#include <bits/stdc++.h>
using namespace std;
int main() {
  int N, M;
  int s, c;
  int flg_ne = 0, ans = 0;
  vector<int> the_num{10, 10, 10};
  std::cin >> N >> M;
  for (int i = 0; i < M; i++) {
    std::cin >> s >> c;
    if (the_num[3 - N + s - 1] == 10) {
      the_num[3 - N + s - 1] = c;
    } else {
      if (the_num[3 - N + s - 1] != c) {
        flg_ne = 1;
        break;
      }
    }
  }
  if (the_num[3 - N] == 0) {
    flg_ne = 1;
  }
  if (the_num[0] == 10) {
    the_num[0] = 1;
  }
  if (the_num[1] == 10) {
    if (N == 2) {
      the_num[1] = 1;
    } else {
      the_num[1] = 0;
    }
  }
  if (the_num[2] == 10) {
    the_num[2] = 0;
  }
  if (flg_ne == 1) {
    std::cout << -1;
  } else {
    if (N == 1) {
      std::cout << the_num[2];
    } else if (N == 2) {
      std::cout << the_num[1] << the_num[2];
    } else if (N == 3) {
      std::cout << the_num[0] << the_num[1] << the_num[2];
    }
  }
}
