#include <bits/stdc++.h>
using namespace std;
int mod = 998244353;
const int M = 1e6 + 10;
const int N = 1e5 + 10;
inline long long read() {
  long long b = 1, sum = 0;
  char c = getchar();
  while (!isdigit(c)) {
    if (c == '-') b = -1;
    c = getchar();
  }
  while (isdigit(c)) {
    sum = sum * 10 + c - '0';
    c = getchar();
  }
  return b * sum;
}
int n, m[4], k, T;
long long ans, yu;
int main() {
  int i, j;
  double r;
  double pi = 3.1415926;
  scanf("%lf", &r);
  printf("%f", r * r * pi);
  return 0;
}
