#############################################################

import sys
sys.setrecursionlimit(10**7)

from heapq import heappop,heappush
from collections import deque,defaultdict,Counter
from bisect import bisect_left, bisect_right
from itertools import product,combinations,permutations

ipt = sys.stdin.readline

def iin():
    return int(ipt())
def lmin():
    return list(map(int,ipt().split()))

MOD = 998244353
#############################################################

N = iin()
for i in range(2,N):
    if N%i == 0:
        continue
    break
print(N-1-i)