#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i, s, e) for (int i = (int)s; i < (int)e; i++)

double pi = 3.141592653589793238;

int main() {
    cin.tie(nullptr);
    
    cout << fixed << setprecision(15);
    
    double C, Rin, Rout;
    cin >> C >> Rin >> Rout;
    
    double r = (Rin + Rout) / 2;
    double rr = (Rout - Rin) / 2;
    
    double ans = C * rr * rr * pi * 2 * pi * r;
    cout << ans << '\n';
}