#define _USE_MATH_DEFINES
#include <cmath>
#include<stdio.h>
#include <vector>
#include <list>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <algorithm>
#include <sstream>
#include <iostream>
#include <string>
#include <stdio.h>

using namespace std;

int main() {

	double C, RI, RO;
	cin >> C >> RI >> RO;

	double r = (RO - RI) / 2.0;

	printf("%.6lf\n", C*r*r*M_PI * 2 * (RI + r) * M_PI);

	return 0;
}