import random
import sys
def is_prime(n):
    if n == 2: return True
    if n == 1 or n & 1 == 0: return False

    d = (n - 1) >> 1
    while d & 1 == 0:
        d >>= 1

    for k in range(10):
        a = random.randint(1, n - 1)
        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

n=int(input())
used=[False for i in range(2002)]
isprime=[False for i in range(2002)]
for i in range(3, 2002, 2):
    isprime[i]=True
isprime[2]=True
for i in range(3, 2002):
    if isprime[i]:
        for j in range(2*i, 2002, i):
            isprime[j]=False

def dfs(x, w):
    used[x]=True
    if x%w!=1 and (not used[x-1]) and (not isprime[x-1]):
        dfs(x-1, w)
    if x%w!=0 and x+1<=n and (not used[x+1]) and (not isprime[x+1]):
        dfs(x+1, w)
    if x>w and (not used[x-w]) and (not isprime[x-w]):
        dfs(x-w, w)
    if x+w<=n and (not used[x+w]) and (not isprime[x+w]):
        dfs(x+w, w)
def solve(w):
    for i in range(1, n+1):
        used[i]=False
    dfs(1, w)
    return used[n]

if n<=2000:
    for i in range(3, n):
        if solve(i):
            print(i)
            sys.exit()
else:
    if n%8!=1:
        print(8)
    elif not is_prime(n-8):
        print(8)
    elif n%14!=1:
        print(14)
    elif not is_prime(n-14):
        print(14)
    else:
        print(17)