#include <bits/stdc++.h>
using namespace std;
int main(void) {
  double ans = 0.0, d, d1, d2;
  long long int m, n, i, j, k = 1;
  long long int a, a1, a2, a3, sum;
  string s, s1, s2;
  char c, c1;
  sum = a = a1 = a2 = a3 = 0;
  cin >> n;
  cout << n * n * 3.1415926;
  return 0;
}
