#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";
    }