#!/usr/bin/env python3
# -*- coding: utf-8 -*-

import random

EXP_TIMES = 50000


def roll_dice(k):
    n = 0
    s = 0
    while True:
        s += random.randint(1, 6)
        n += 1
        if s == k:
            return n
        elif s < k:
            continue
        else:
            s = 0
            continue


def get_expectation(k, e=EXP_TIMES):
    return sum(float(roll_dice(k)) for i in range(EXP_TIMES)) / float(e)


def main():
    print(get_expectation(int(input())))

if __name__ == "__main__":
    main()