#include <bits/stdc++.h>
using namespace std;
int binarySearch(int arr[], int l, int r, int x) {
  if (r >= l) {
    int mid = l + (r - l) / 2;
    if (arr[mid] == x) return mid;
    if (arr[mid] > x) return binarySearch(arr, l, mid - 1, x);
    return binarySearch(arr, mid + 1, r, x);
  }
  return l;
}
void swap(long long int *p1, long long int *p2) {
  long long int temp = *p1;
  *p1 = *p2;
  *p2 = temp;
}
int main() {
  long long int n;
  cin >> n;
  cout << 3.14159265358979 * n * n;
}
