#include <iostream>
#include <cmath>
#define pi 3.141592653
using namespace std;

int main()
{
    double c,ri,ro;
    cin >> c >> ri >> ro;

    double nagasa = ((2*ri*pi) + (2*ro*pi)) / 2;
    double enn = pow(((ro - ri) / 2),2) * pi;
    
    cout << fixed << nagasa * enn * c << endl;

    return 0;
}