asd

setasd

#include <iostream>
#include <vector>
using namespace std;

int main()
{
	double h=0;
	double p1, p2, p3;
	int n;
	cin >> p1;
	cin >> p2;
	cin >> p3;
	cin >> n;
	if (n/5 <1)
		h = h + p1*p3 + (1 - p3)*(1 - p2);
	else if ((n/5) %2 !=0 )
		h = p1*(1 - p3) + (p3)*(1 - p2);
	else 
		h = h + p1*p3 + (1 - p3)*(1 - p2);
	cout << h << endl;
	//cin >> h;
}