UVa 10286 - Trouble with a Pentagon

// UVa 10286 - Trouble with a Pentagon

#include <cmath>
#include <stdio.h>
#include <iostream>
using namespace std;

int main() {
	double a;
	double c = sin(108 * M_PI / 180) / sin(63 * M_PI / 180);
	while (cin >> a) {
		double b = a * c;
		printf("%.10f\n", b);
	}
	return 0;
}