#include<stdio.h>
#include<math.h>
main(){
    int C,Ri,Ro;
    scanf("%d%d%d",&C,&Ri,&Ro);
    double r = (Ro-Ri)/2.,R = Ri+r;
    printf("%lf\n",2*M_PI*M_PI*r*r*R*C);
}