#include<bits/stdc++.h> using namespace std; int main() { int a,b,x,y; cin>>x>>a>>y>>b; int z=(b*y-a*x)/(b-a); cout<<(z); double value = z; std::string str = std::to_string(value); std::string result = str.substr(0, str.find('.') + 3); std::cout << result << std::endl; return 0; }