#include <iostream>
#include <algorithm>
#include <vector>
#include <string>
#include <cmath>
#include <iomanip>
using namespace std;
typedef long long LL;

int main(){
    double C, r1, r2;
    cin >> C >> r1 >> r2;
    double R = (r1 + r2) * 0.5;
    double r = (r2 - r1) * 0.5;
    cout << setprecision(13) << C * 2.0 * M_PI * M_PI * r * r * R << endl;
    return 0;
}