#include<bits/stdc++.h> using namespace std; int main(){ float x,a,y,b; cin>>x>>a>>y>>b; cout<<fixed<<setprecision(2)<<(xa-yb)/(a-b); return 0; } //printf("%.3f\n",a);//C语言 //cout<<fixed<<setprecision(2)<<a;//C+