//No.89 どんどんドーナツどーんといこう！
#include <iostream>
#include <iomanip>
#include <cmath>

using namespace std;

const double PI = acos(-1);

signed main(){
    int c , ri , ro;
    cin >> c >> ri >> ro;
    double v =  PI * PI * (ro + ri) * ( ro - ri) * ( ro - ri) / 4.0;
    cout << fixed << setprecision(16) << c * v << endl;
}