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