#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); ++i)
int main() {
    // Input
    double C, Rin, Rout;
    cin >> C >> Rin >> Rout;

    // Output
    double r = (Rout - Rin) / 2.0;
    double R = (Rout + Rin) / 2.0;
    double PI = acos(-1);
    cout << fixed << setprecision(20);
    cout << 2.0 * PI * PI * r * r * R * C << endl;
}