#!/usr/bin/env python3
def is_prime(n):
    if n**0.5 < 10**5:
        if n == 1:
            return False
        for i in range(2, int(n**0.5)+1):
            if n % i == 0:
                return False
        return True
    else:
        import subprocess
        factors = list(map(int,subprocess.check_output(['factor', str(n)]).split()[1:]))
        return len(factors) == 1
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())))