#include <bits/stdc++.h>
#define rep(i,n) for (int i = 0; i < (n); i++)
using namespace std;
using ll = long long;
using P = pair<int,int>;

int main() {
  int n, m;
  cin >> n >> m;
  int a[3]={0,0,0};
  rep(i,m) {
    int s, c;
    cin >> s >> c;
    if(n!=1&&s==1&&c==0) {
      cout << -1 << endl;
      return 0;
    }
    if(a[s-1]!=0&&a[s-1]!=c) {
      cout << -1 << endl;
      return 0;
    }
    a[s-1] = c;
  }
  if(n!=1&&a[0]==0) a[0]=1;
  rep(i,n) cout << a[i];
  cout << endl;
}
