#include <stdio.h>
#include <math.h>
#include <stdlib.h>

/* pointer love */
double entropy (double *p) {
  double v = *p;
  return (log(v)/v*log(v));
}

int main() {
  double *i = (double*) malloc(sizeof(double));
  scanf("%d", i);
  printf("%d\n",entropy(i));
}