#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <iomanip>
#include <stack>
#include <algorithm>
#include <string>
#include <map>
#include <iterator>
#include <set>
#include <queue>
#include <bitset>
#include <cassert>

using namespace std;

int main() {
    double PI = 3.141592653589793238462643383279;
    double C;
    cin >> C;
    double Ri, Ro;
    cin >> Ri >> Ro;

    double a = (Ro - Ri) / 2.0;
    double b = (Ro + Ri) / 2.0;

    cout << fixed << setprecision(10) << PI * a * a * 2.0 * PI * b * C << endl;

}