#include <iostream>
#include <cstring>
#include <cmath>
#include <iomanip>
using namespace std;

int main(){
	double a,b,c;
	double pi=3.1415926535898;
	cin >> a >> b >> c;
	cout << fixed;
	cout << setprecision(10) << (a*(c-b)*(c-b)/4*pi*(c+b)*pi);
	return 0;
}