#include<bits/stdc++.h>
using namespace std;
int main(){
	double n;
	cin >>n;
	printf("%0.2lf",n*3.14*4/3*n*n);
	return 0;
}

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

int main(){ double r,v; cin>>r; v=4.0/33.14rrr; cout<<fixed<<setprecision(2)<<v; return 0; }