#include <iostream>
#include <algorithm>
#include <cstdio>
#include <cmath>

const long double PI = acos(-1);

using namespace std;

int main()
{
    double C, Rin, Rout;
    cin >> C >> Rin >> Rout;
    double h = (Rout - Rin) / 2;
    double ans = C * (2 * h * h * (h + Rin) * PI * PI);    

    printf("%lf\n", ans);

    return 0;
}