#include <iostream>
#include <sstream>
#include <math.h>
#include <stack>
#include <set>
#include <algorithm>
#include <string>
#include <queue>
#include <stack>
#include <map>
#include <cstdio>
#include <vector>
#include <iomanip>
using namespace std;

#define INF (1 << 30)
#define INFLL (1LL << 60)

#define PI 3.14159265359

int main() {
	double c,a,b;
	cin >> c >> a >> b;
	b = (b - a) / 2;
	a = (a + b);
	cout << fixed << setprecision(6);
	cout << (b*b*PI)*(2*a*PI)*c << endl;
	return 0;
}