#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m, i, j;
  cin >> n >> m;
  vector<int> A(n, 16);
  vector<int> S(m);
  vector<int> C(m);
  for (i = 0; i < m; i++) cin >> S[i] >> C[i];
  int ch = 0;
  if (n == 1) {
    for (i = 0; i < m; i++) {
      if (A[0] != 16) {
        if (A[0] != C[i])
          ch = 1;
        else
          ch = 0;
      } else
        A[0] = C[i];
    }
    if (ch == 1)
      cout << -1 << endl;
    else
      cout << A[0] << endl;
  } else {
    for (i = 0; i < m; i++) {
      if (S[i] == 1 && C[i] == 0)
        ch = 1;
      else if (A[S[i] - 1] != 16) {
        if (A[S[i] - 1] != C[i])
          ch = 1;
        else
          ch = 0;
      } else
        A[S[i] - 1] = C[i];
    }
    for (i = 0; i < n; i++) {
      if (i == 0 && A[i] == 16)
        A[i] = 1;
      else if (A[i] == 16)
        A[i] = 0;
    }
    if (ch == 1)
      cout << -1 << endl;
    else {
      for (i = 0; i < n; i++) {
        cout << A[i];
      }
      cout << endl;
    }
  }
}
