#include <cstdio>
#include <iostream>
#include <cmath> // M_PI
using namespace std;

int main() {
    int c, rin, rout;
    scanf("%d %d %d", &c, &rin, &rout);

    double r = (rout - rin) / 2.0;
    double area = r * r * M_PI;
    double cir = 2 * M_PI * (rin + r);

    double ans = c * area * cir;
    printf("%lf\n", ans);

}