#include <bits/stdc++.h>
using namespace std;
double EPS = 1e-9;
int INF = 1000000005;
long long INFF = 1000000000000000005LL;
inline void OPEN() {}
void solve() {
  long long r;
  cin >> r;
  cout << 2 * 3.141592653589793238 * r * r << "\n";
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  ;
  solve();
  return 0;
}
