#define _CRT_SECURE_NO_WARNINGS
#define _USE_MATH_DEFINES
#include <iostream>
#include <map>
#include <list>
#include <cstdio>
#include <cmath>
#include <cstring>
#include <string>
#include <vector>
#include <algorithm>
#include <utility>
#include <queue>
#include <iomanip>

using namespace std;

int main()
{
	double C;
	double Rin, Rout;
	double r1, r2;
	double res;


	cin >> C >> Rin >> Rout;

	r1 = (Rout - Rin) / 2;
	r2 = (Rout - Rin) / 2 + Rin;

	res = (r1 * r1 * M_PI) * (M_PI * r2 * 2) * C;

	cout << fixed << setprecision(10) << res << endl;

	return (0);
}