6

#include <bits/stdc++.h>
#define endl "\n"
using namespace std;
double a,b,c,d;
double f(double x){
	return a*x*x*x+b*x*x+c*x+d;
}
int main(){
	ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
	//freeopen(".in","r",stdin);
	//freeopen(".out","w",stdout);
	cin>>a>>b>>c>>d;
	double l=0,r=100,mid1,mid2;
	while(r-l>1e-10){
		mid1=l+(r-l)/3;
		mid2=l+(r-l)*2/3;
		if(f(mid1)>f(mid2)) l=mid1;
		else         r=mid2;
	}
	cout<<fixed<<setprecision(10)<<(l+r)/2;
	return 0;
}