#include <bits/stdc++.h>
using namespace std;
int main() {
  int n,m,y,z;
  cin >> n >> m;
  vector<int> x(n,10);
  for (int i = 0; i < m; i++) {
    cin >> y >> z;
    if(y==1&&z==0&&n!=1) {
      cout << -1 << endl;
      exit(0);
    }
    if(x[y-1]!=10&&x[y-1]!=z) {
      cout << -1 << endl;
      exit(0);
    }
    x[y-1]=z;
  }
  if(x[0]==10) {
    if(n!=1){
      x[0]=1;
    }else{
      x[0]=0;
    }
  }
  for (int i = 0; i < n; i++) {
    cout << x[i]%10;
  }
  cout << endl;
}