#include<iostreram>
#include<cmath>
using namespace std;

class Area{
    public:
    double area(double s){
        return s>0?s*s-1;
        
    }
    double area(double i,double w){
       return (i>0&&w>0)? i*w : -1;
       
    }
    double area(int r){
        return r>0 ? M PI*r*r:-1;
    }
};
int main(){
    int t;
    cin>>t;
    Area a;
    double ans= -1;
    if(t==1){
        cin>>x;
        ans=a.area(x);
        
    }
    else if(t==2){
        cin>>x>>y;
        ans=a.area(x,y);
    }
    else if(t==3){
        cin>>r;
        ans=a.area(r);
    }
    else ans=-1;
}
if(ans==-1)
cout<<"Invalid input";
else
cout<<ans;
}