#include <bits/stdc++.h>
using namespace std;

template<typename T>
istream &operator>>(istream &is,vector<T> &a){
    for(auto &v : a) cin >> v;
    return is;
}
template<typename T>
ostream &operator<<(ostream &os,const vector<T> &a){
    if(a.size() == 0) return os;
    cout << a.at(0);
    for(int i=1; i<a.size(); i++) cout << " " << a.at(i);
    cout << "\n";
    return os;
}

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    double pi = M_PI;

    double C,r,R; cin >> C >> r >> R;
    R -= r,R /= 2,r += R,r *= pi*2,R *= R*pi;
    cout << fixed << setprecision(20) << r*R*C << endl;

}