#include<iostream>
#include<string>
#include<algorithm>
#include<functional>
#include<vector>
#include<queue>
#include<stack>
#include<set>
#include<map>
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<math.h>
using namespace std;
#define PAI 3.1415926

double c,rin,rout;

int main(){
	cin >> c >> rin >> rout;
	printf("%f\n", ( (PAI*(rout-rin)*(rout-rin)/4.0) * ( 2.0 * PAI * (rout+rin)/2.0 ) ) * c );
	return 0;
}