#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <cmath>
#include <string>
#include <vector>
#include <algorithm>
#include <queue>
#include <map>
#include <functional>
#include <set>
#include <numeric>
#include <stack>
#include <utility>
//#include "util.h"

using namespace std;
typedef long long lint;
typedef pair<lint, lint> Pii;

#define PI 3.14159265358979323846

int main()
{
	double C, Ri, Ro, r, R;
	cin >> C >> Ri >> Ro;
	r = (Ro - Ri) / 2;
	R = (Ro + Ri) / 2;
	printf("%.10f\n", 2 * PI * PI * r * r * R * C);
	return 0;
}