#include <stdio.h>
double my_sqrt(double num)
{
  double root, root_n = 1.0;
  do {
    root = root_n;
    root_n = (root + num / root) / 2;
  } while(root_n != root);
  return root;
}
int main()
{
  double num;
  scanf("%lf", &num);
  printf("%lf\n", my_sqrt(num));
  return 0;
}