#include <bits/stdc++.h> 

using namespace std;
typedef long long ll;

int main() {
    // double C, Rin, Rout;
    // cin >> C >> Rin >> Rout;

    // double r = (double)((Rout - Rin) * 0.5);
    // double rr = (double)Rin + r;
    // double PI = 3.141592;
    // cout << r << endl;
    // cout << rr << endl;
    // cout << PI << endl;
    // cout << (double)C << endl;
    // double cal = (double) C * r * r * PI * 2.0 * PI * rr;
    // cout << setprecision(6) << cal << endl;

    double pi = acos(-1);
    int c, a, b;
    cin>>c>>a>>b;
    double r = (b-a)/2.0;
    cout << pi * r * r * (a+b) * pi * c << endl;
    return 0;
}