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

int main(){  
    double C, Rin, Rout; cin >> C >> Rin >> Rout;
    cout << fixed << 2 * (M_PI) * (M_PI) * pow((Rout-Rin) / 2, 2.0) * (Rin + (Rout - Rin) / 2) * C << endl;
    return 0;
}