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

int main(){
	double c,r1,r2; cin>>c>>r1>>r2;
	double r=(r2-r1)/2;
	double area=r*r*M_PI;
	double g=(r1+r)*2*M_PI;
	double ans=area*g*c;
	printf("%.8f\n",ans);
}