#include <iostream>
#include <string>
#include <map>
#include <cmath>
#include <vector>

using namespace std;

int main(void){
	double c,ri,ro;
	cin >> c >> ri >> ro;
	double r = (ro-ri)/2.;
	printf("%.10f\n",M_PI * r*r * 2 * M_PI * (ri+r) * c);
	return 0;
}