import sys

sys.setrecursionlimit(10**7)
def I(): return int(sys.stdin.readline().rstrip())
def MI(): return map(int,sys.stdin.readline().rstrip().split())
def LI(): return list(map(int,sys.stdin.readline().rstrip().split()))
def LI2(): return list(map(int,sys.stdin.readline().rstrip()))
def S(): return sys.stdin.readline().rstrip()
def LS(): return list(sys.stdin.readline().rstrip().split())
def LS2(): return list(sys.stdin.readline().rstrip())


def sieve_of_eratosthenes(n):  # n以下の素数の全列挙
    prime_list = []
    A = [1]*(n+1)  # A[i] = iが素数なら1,その他は0
    A[0] = A[1] = 0
    for i in range(2,int(n**.5)+1):
        if A[i]:
            prime_list.append(i)
            for j in range(i**2,n+1,i):
                A[j] = 0
    for i in range(int(n**.5)+1,n+1):
        if A[i] == 1:
            prime_list.append(i)
    return prime_list


N = I()
primes = sieve_of_eratosthenes(N)

dp = [-1]*(N+1)
dp[0] = (0,0)
inf = 10**18
for i in range(1,N+1):
    count = 0
    prime = inf
    for p in primes:
        if p > i:
            break
        if dp[i-p] == -1:
            continue
        a,b = dp[i-p]
        if p <= b or a+1 < count:
            continue
        if a+1 == count:
            prime = min(prime,p)
        elif a+1 > count:
            count = a+1
            prime = p
    if count == 0:
        dp[i] = -1
    else:
        dp[i] = (count,prime)

ans = dp[-1]
if ans == -1:
    print(-1)
else:
    print(ans[0])