Задача L. Улитки

#define _CRT_SECURE_NO_WARNINGS
#define _USE_MATH_DEFINES
#include <iostream>
#include <conio.h>
#include <string>
#include <algorithm>
#include <vector>
#include <map>
#include <queue>
#include <set>
#include <stack>

using namespace std;

typedef long long ll;

int main()
{
    ll n, a, v;
    cin >> n >> a >> v;

    double answ;
    double A = ((90 * (n - 2)) / (n*1.0))*(M_PI/180);
    double r = a / (2 * sin(M_PI / (n*1.0)));

    answ = r/(v*cos(A)*1.0);
    printf("%.6lf", v*answ*n);
    _getch();
    return 0;
}