---

#include <iostream>
using namespace std;

int main() {
    int element;
    double value, S;
    const double PI = 3.14159;
    
    cout << "Chto izvestno? (1-radius, 2-diametr, 3-dlina okruzhnosti): ";
    cin >> element;
    
    cout << "Vvedite znachenie: ";
    cin >> value;
    
    switch (element) {
        case 1:
            // S = PI * R^2
            S = PI * value * value;
            cout << "Ploshchad kruga: " << S << endl;
            break;
        case 2:
            // S = PI * D^2 / 4
            S = PI * (value * value) / 4.0;
            cout << "Ploshchad kruga: " << S << endl;
            break;
        case 3:
            // S = L^2 / (4 * PI)
            S = (value * value) / (4.0 * PI);
            cout << "Ploshchad kruga: " << S << endl;
            break;
        default:
            cout << "Nevernyy nomer elementa!" << endl;
    }
    
    return 0;
}