#include <bits/stdc++.h>

using namespace std;

int main()
{

    int n,m;
    cin >> n >> m;
    int a[n] = {0};
    int s,c;
    for(int i=0;i<m;i++){
        cin >> s >> c;
        a[s-1] = c;
    }
    if(n==3 && a[0]==0)
        cout << -1;
  	else if(n==2 && (a[1]==0 || a[0]>0))
      	cout << -1;
    else
        if(n==1)
            cout << a[2];
        else if(n==2)
            cout << a[1] << a[2];
        else
            cout << a[0] << a[1] << a[2];
    return 0;
        
}