DTTRON C++

#include <bits/stdc++.h>
using namespace std;

int r;
float s;

int main()
{
    freopen("dttron.inp","r",stdin);
    freopen("dttron.out","w",stdout);
    cin>>r;
    s=r*r*3.14;
    cout<<fixed <<setprecision(2);
    cout<<s;
}