#include<stdio.h>
#include<algorithm>
using namespace std;
double PI=3.14159265359;
int main(){
	double a,b,c;
	scanf("%lf%lf%lf",&a,&b,&c);
	double s=(c-b)*(c-b)*PI/4;
	double t=(b+c)*PI;
	double v=s*t;
	printf("%.12f\n",v*a);
}