#!/usr/bin/env python3
import random
def is_prime(n, k=20): # miller-rabin primality test
    if n == 2:
        return True
    if n == 1 or n % 2 == 0:
        return False
    d = n - 1
    while d % 2 == 0:
        d //= 2
    for _ in range(k):
        a = random.randint(1,n-2)
        t = d
        y = pow(a,t,n)
        while t != n-1 and y != 1 and y != n-1:
            y = (y * y) % n
            t <<= 1
        if y != n-1 and t & 1 == 0:
            return False
    return True
def bfs(n, w, initial, accept, deny=None):
    que = [initial]
    i = 0
    pushed = set(que)
    while i < len(que):
        if accept(que, i):
            return True
        if deny is not None and deny(que, i):
            return False
        x = que[i]
        i += 1
        def f(y):
            if y not in pushed and not is_prime(y):
                que.append(y)
                pushed.add(y)
        if x-1 >  0 and x % w != 1: f(x-1)
        if x+1 <= n and x % w != 0: f(x+1)
        if x-w >  0:                f(x-w)
        if x+w <= n:                f(x+w)
def solve(n):
    if n < 300: # magic number
        for w in range(1,n):
            if bfs(n, w, 1, lambda que, i: que[i] == n):
                return w
    else:
        for w in range(2,n):
            if bfs(n, w, 1, lambda que, i: que[i] % w == 0) \
                    and bfs(n, w, n, lambda que, i: len(que) >= 10): # magic number
                return w
print(solve(int(input())))