#include<bits/stdc++.h>
using namespace std;
double f(double x,double a,double b){
    return x*x+a*x+b;
}
int main(){
    int a,b,c,d;
    cin>>a>>b>>c>>d;
    double l=c,r=d;
    while(r-l>0.00000001){
        double m=(l+r)/2;
        if(f(l,a,b)*f(m,a,b)<0){
            r=m;
        }
        else{
            l=m;
        }
    }
    cout<<fixed<<setprecision(6)<<l;
    return 0;
}