#include <stdio.h>

int main(void){
    int C, Ri, Ro;
    double r, pi = 3.141592653589793238462643383279;
    scanf("%d", &C);
    scanf("%d %d", &Ri, &Ro);
    r = (Ro-Ri) / 2.0;
    printf("%lf\n", 2*r*r*(Ri+r)*pi*pi*C);
    return 0;
}