#define _USE_MATH_DEFINES
#include<iostream>
#include<vector>
#include<algorithm>
#include<cmath>
#include<string>
#include<iomanip>
#include<numeric>
#include<queue>
#include<deque>
#include<stack>
#include<set>
#include<map>
#include<random>
using namespace std;
typedef long long ll;
const int mod=1e9+7;
int main(){
	double c,rin,rout;
	cin>>c>>rin>>rout;
	cout<<fixed<<setprecision(20)<<(rin+rout)*M_PI*pow((rout-rin)/2,2)*M_PI*c<<endl;
}