#include <iostream> using namespace std; int main() { double x,y,a,b,ziyuan,c[10],d[10]; int i=1,t,f; cin>>x>>a>>y>>b; ziyuan=(b*y-a*x)/(b-a); t=ziyuan*100; f=ziyuan*1000; while(t>0){ c[i]=t%10; i++; t=t/10; } for(int j=i-1;j>=3;j--){ cout<<c[j]; } cout<<"."<<c[2]; if(f%10>=5) cout<<c[1]+1; else cout<<c[1]; }