#include<bits/stdc++.h>
using namespace std;
int main(){
    int x,y,z,w,c;
    cin>>x>>y>>z>>w;
    if(z==0||w==0){
       if(z==0&&w==0)
        {cout<<-1;
	   }
       else if(z==0){
	   if(x!=0||y==0||y%w!=0)
	   {
	   cout<<-1;
	   }
	   else cout<<y/w;
	   }
	   else if(w==0) 
	   {
	   if(y!=0||x==0||x%z!=0)
	   {
	   	cout<<-1;
	   }
	   }
        else cout<<x/z;
	}else if((x/z==y/w)&&(x%z==0)&&(y%w==0)){
	   cout<<y/w;
    }else{
        cout<<-1;
    }
}