#include<iostream>
#include<string>
#define _USE_MATH_DEFINES
#include<math.h>
#include<iomanip>
using namespace std;

int main(){
	double c;
	double rin;
	double rout;
	cin >> c;
	cin >> rin;
	cin >> rout;
	long double ans = (pow((rout - rin) / 2, 2)*M_PI)*((rout+rin)*M_PI)*c;
	cout << setprecision(16) << ans << endl;
	return 0;
}