#include "bits/stdc++.h"
using namespace std;



int main(){
	double C;
	double rin, rout;
	cin >> C;
	cin >> rin >> rout;
	double R = (rout - rin) / 2;
	double D = (rin + rout) / 2;
	double PI = 3.141592653589793238462643383279;
	double ans = R * R * PI * 2 * PI * D * C;
	printf("%.14f\n", ans);
}