#include<iostream>
#include<iomanip>
using namespace std;
int main(){
    int a,b,c;
    cin>>a;
    if(a<=0){
        cout<<"Invalid input";
        return 0;
    }
    switch(a){
        case 1:
        cin>>b;
        if(b<0){
            cout<<"Invalid input";
        }else{ cout<<b*b; }
        break;
        
        case 2:
        cin>>b;
        cin>>c;
        if(b<0 ||c<0){
            cout<<"Invalid input";
        }else { cout<< b*c;}
        break;
        
        case 3:
        cin>>b;
        if(b<0){
            cout<<"Invalid input";
        }else{ cout<<(M_PI)*pow(b,2); }
        break;
        
        default:
        cout<<"Invalid input";
        }
    }
    return 0;
}