#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;


int main() {
   int a,b,c,d;
    cin>>a>>b>>c>>d;
    if((a==b)&&(b==c)&&(c==d)&&(d==a))
        {
        cout<<"1";
    }
    else
        cout<<"-1"<<endl;
    return 0;
}