#define _USE_MATH_DEFINES

#include <iostream>		//cin, cout
#include <vector>		//vector
#include <algorithm>	//sort,min,max,count
#include <string>		//string,getline, to_string
#include <cstdlib>		//abs(int)
#include <utility>		//swap, pair
#include <deque>		//deque
#include <climits>		//INT_MAX
#include <bitset>		//bitset
#include <cmath>		//sqrt, ceil. M_PI, pow, sin
#include <ios>			//fixed
#include <iomanip>		//setprecision
#include <sstream>		//stringstream
#include <numeric>		//gcd, assumlate
#include <random>		//randam_device
#include <limits>		//numeric_limits

using namespace std;
constexpr long long int D_MOD = 1000000007;

inline double CalcTorus(const double rin, const double rout) {
	//円環体(トーラス)の体積を計算する
	double ans = M_PI * M_PI * (rin + rout) * (rout - rin) * (rout - rin) / 4;
	return ans;
}

int main() {

	int C;
	cin >> C;

	double Rin, Rout;
	cin >> Rin >> Rout;

	double ans = CalcTorus(Rin, Rout) * C;

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

	return 0;

}