#include <iostream>#include <cstdio>#include <cmath>#include <cstring>#include <algorithm>using namespace std;typedef long long LL;int R , r , H , F , S;double radius , ans , height , dr , pi = acos(-1.);double check(){ int top = 3 , mid , bot = 1e5; double res = 1e60; while (top < bot) { mid = top + bot + 1 >> 1; double theta = pi / mid; double area = (2 * radius * tan(theta)) * height; if (area >= S) top = mid , res = area * mid; else bot = mid - 1; } return res;}void work(){ ans = 0 , height = 1. * H / F , dr = 1. * (R - r) / F , radius = r; for (int i = 0 ; i < F ; ++ i , radius += dr) ans += check(); printf("%fn" , ans);}int main(){ while (~scanf("%d%d%d%d%d",&R , &r , &H , &F , &S)) work(); return 0;}
