from random import randint
from collections import deque
from math import sqrt
n = input()

M = min(1003, n)
prime = [1]*(M+1)
prime[0] = prime[1] = 0
p_num = 0
for i in xrange(2, int(sqrt(M))+1):
    if prime[i]:
        for j in xrange(i*i, M+1, i):
            prime[j] = 0

def fermat(k):
    for t in xrange(1000):
        a = randint(2, k-1)
        if pow(a, k-1, k)!=1:
            return 0
    return 1

i = 2
while i<=40:
    deq = deque()
    deq.append(1)
    used = [0]*(M+1)
    ok = 0
    while deq:
        v = deq.popleft()
        if n>M and v%i==0:
            ok = 1
            break
        if v==n:
            print i
            exit(0)
        if v+1 <= M and v%i!=0 and not prime[v+1] and not used[v+1]:
            used[v+1] = 1
            deq.append(v+1)
        if v-1 >= 1 and v%i!=1 and not prime[v-1] and not used[v-1]:
            used[v-1] = 1
            deq.append(v-1)
        if v+i <= M and not prime[v+i] and not used[v+i]:
            used[v+i] = 1
            deq.append(v+i)
        if v-i >= 1 and not prime[v-i] and not used[v-i]:
            used[v-i] = 1
            deq.append(v-i)
    if ok:
        if (n%i!=1 and not fermat(n-1)) or not fermat(n-i):
            print i
            exit(0)
    i += 1
exit(1)