/* -*- coding: utf-8 -*-
 *
 * 1076.cc:  No.1076 寿司打 - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int CNT = 1000000;

/* typedef */

/* global variables */

/* subroutines */

/* main */

int main() {
  double p;
  scanf("%lf", &p);

  double sum = 0.0, q = p;
  for (int i = 1; i <= CNT; i++) {
    sum += q * i;
    q *= p;
  }

  printf("%.10lf\n", sum * (1.0 - p));
  return 0;
}