#include<bits/stdc++.h>
using namespace std;
const double pi=3.1415926535897932384626;
int main()
{
	int x,y;
	cin>>x>>y;
	double t,v;
	cin>>t;
	cin>>v;
	double num=t*v;
	double ans2=sqrt(pow(x,2)+pow(y,2));
	double ans3=2*pi*ans2;
	double ans1=(num-int(t*v))*ans2*(1/(num-int(t*v))*2);
	if((num-int(t*v))*ans3==0)
		printf(0);
	else
		printf("%.10f",ans1);
	return 0;
}