# region template
from typing import Generic, Iterable, Iterator, TypeVar, Union, List
from bisect import bisect_left, bisect_right
from bisect import bisect_left, bisect_right, insort
from email.policy import default
import re
import typing
import math
import sys
import copy
import itertools
import collections
import bisect
import heapq
import decimal
import random
import gc


def ni(): return int(sys.stdin.readline())
def ns(): return map(int, sys.stdin.readline().split())
def ns1(): return map(lambda x: int(x)-1, sys.stdin.readline().split())
def na(): return list(map(int, sys.stdin.readline().split()))
def na1(): return list(map(lambda x: int(x)-1, sys.stdin.readline().split()))
def nall(): return list(map(int, sys.stdin.read().split()))
def flush(): return sys.stdout.flush()
def nib(): return int(sys.stdin.buffer.readline())
def nsb(): return map(int, sys.stdin.buffer.readline().split())
def ns1b(): return map(lambda x: int(x)-1, sys.stdin.buffer.readline().split())
def nab(): return list(map(int, sys.stdin.buffer.readline().split()))
def na1b(): return list(map(lambda x: int(x)-1, sys.stdin.buffer.readline().split()))
def nallb(): return list(map(int, sys.stdin.buffer.read().split()))
# limregion


# sys.setrecursionlimit(10**7+1)
inf = 10**20
# mod = 10**9+7
mod = 998244353


def main():
    N = ni()
    for i in range(1, N*N+1):
        if i % 7 == 0:
            N += 6
        N -= 1
        if N <= 0:
            print(i)
            break


if __name__ == '__main__':
    main()