import random

def is_prime(n):
    if n < 2:
        return False
    for p in [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37]:
        if n % p == 0:
            return n == p
    d = n - 1
    s = 0
    while d % 2 == 0:
        d //= 2
        s += 1
    for a in [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37]:
        if a >= n:
            continue
        x = pow(a, d, n)
        if x == 1 or x == n - 1:
            continue
        for _ in range(s - 1):
            x = pow(x, 2, n)
            if x == n - 1:
                break
        else:
            return False
    return True

def find_min_w(n):
    for w in range(2, n):
        h = n // w
        r = n % w
        if r == 0:
            last_row_start = h * w - w + 1
            last_row_end = n
        else:
            last_row_start = h * w + 1
            last_row_end = n
        vertical_path = [1 + i * w for i in range(h + 1)]
        vertical_valid = all(not is_prime(num) for num in vertical_path)
        if not vertical_valid:
            continue
        last_row = list(range(last_row_start, last_row_end + 1))
        if all(not is_prime(num) for num in last_row):
            return w
    return n - 1

n = int(input())
print(find_min_w(n))