#include <stdio.h>

int main(void){
    int C, Ri, Ro;
    double r, pipi = 9.8696044010893586188344909998762;
    scanf("%d", &C);
    scanf("%d %d", &Ri, &Ro);
    r = (Ro-Ri) / 2.0;
    printf("%lf\n", 2*r*r*(Ri+r)*pipi*C);
    return 0;
}