#include <bits/stdc++.h>
#define PI 3.14159265359
using namespace std;
int main()
{
    int n, in, out;
    double r;
    cin >> n >> in >> out;

    r = (out-in)/2.0;
    cout << fixed << setprecision(5) << n*(r*r)*2*(in+r)*(PI*PI) << endl;
    return 0;
}