import sys
import math

N=input()

isok=[0]*100
vis=[0]*100
for i in range(2,100):
	for j in range(2,i):
		if i%j==0:
			isok[i]=1

def ok(N,M):
	q=[1]
	while len(q) > 0:
		v = q[-1]
		q.pop()
		
		for t in (v-1,v+1,v-M,v+M):
			if v%M==1 and t==v-1:
				continue
			if v%M==0 and t==v+1:
				continue
			if t<=0 or t>N:
				continue
			if isok[t] and vis[t]<M:
				vis[t]=M
				q.append(t)
	
	if vis[N]==M:
		return 1
	return 0


if N>=50:
	print 8
else:
	for M in range(2,50):
		if ok(N,M):
			print M
			break