#include <bits/stdc++.h>
using namespace std;

int main()
{
	int C, Rin, Rout;
	cin >> C >> Rin >> Rout;

	long double r = Rout - Rin;
	r /= 2;
	long double area = r * r * M_PI;
	long double R = Rout - Rin;
	R = Rin + R / 2;
	long double ans = area * R * 2 * M_PI * C;

	cout << fixed << setprecision(12) << ans << endl;
}