#include<iostream>
#include<cmath>
using namespace std;
class AreaCalculator{
    public:
    double area(double side){
        if(side < 0 || side > 1000)
        throw invalid_argument("invalid input");
        return side*side;
    }
    double area(double length,double width){
        if(length < 0 || width < 0 || length > 1000 || width > 1000)
        throw invalid_argument("invalid input");
        return length*width;
    }
    double area(int radius){
        if(radius <= 0|| radius > 1000)
        throw invalid_argument("invalid input")
        return M_PI*radius*radius;
    }
};
int main()
int t;
cin >> t;
Area Calculator calc;

try{
    switch(t){
        case 1:{
            double side;
            cin >> side;
            cout << calc.area(side);
            break;
        }
        case 2:{
            double length,width;
            cin >> length >> width;
            cout << calc.area(length,width);
            break;
        }
        case 3:{
            int radius;
            cin >> radius;
            cout << calc.area(radius);
            break;
    }
    default:
    cout << "invalid input";
}
}catch(invalid_argument&){
    cout << "invalid input";
}
return 0;
}