#define _USE_MATH_DEFINES
#include<stdio.h>
#include<string>
#include<iostream>
#include<cctype>
#include<cstdio>
#include<vector>
#include<stack>
#include <algorithm>
#include<math.h>
#include<set>
#include<map>
#include<iomanip>

//#include<bits/stdc++.h>



using namespace std;




int main() {
	
	double c,x,y;
	cin>>c>>x>>y;
	double a=y-x;
	a/=2;
	double b=a+x;
	cout<<setprecision(30);
	cout<<a*a*b*M_PI*M_PI*c*2<<endl;
	return 0;
}