#include<iostream>
#include<cmath>
double calculateArea(double side){
    if (side<0){
        return -1.0;
    }
    return side*side;
}
double calculateArea(double length,double width){
    if (length<0||width<0){
        return -1.0;
    }
    return length * width;
}
double calculateArea(float radius){
    if (radius<0){
        return -1.0;
    }
    return PI*radius*radius;
}
int main(){
    int t;
    std::cin>>t;
    double result;
    if (t==1){
        double side;
        std::cin>>side;
        result=calculateArea(side);
    }else if (t==2){
        double length, width;
        std::cin>>length>>width;
        result=calculateArea(length, width);
}else if (t==3){
        float radius;
        std::cin>>radius;
        result=calculateArea(radius);
}else{
    std::cout<<"Invalid input"<<std::endl;
    return 0;
}
if (result== -1.0){
    std::cout<<"Invalid input"<<std::endl;
}else{
    std::cout<<result<<std::endl;
}
    return 0;
}