#include <stdio.h>

int main(){
    int cal, Rin, Rout;
    double pi = 3.14159265359, Rmid, Rcir, height, area;
    scanf("%d%d%d", &cal, &Rin, &Rout);
    Rmid = (Rin + Rout)/2.0;
    height = Rmid * 2 * pi;
    Rcir = Rout - Rmid;
    area = Rcir * Rcir * pi;
    printf("%lf\n", area * height * cal);

    return 0;
}