def get_sieve_of_eratosthenes_new(n):
    import math
    if not isinstance(n, int):
        raise TypeError('n is int type.')
    if n < 2:
        raise ValueError('n is more than 2')
    prime = []
    limit = math.sqrt(n)
    data = [i + 1 for i in range(1, n)]
    while True:
        p = data[0]
        if limit <= p:
            return prime + data
        prime.append(p)
        data = [e for e in data if e % p != 0]

N=int(input())
if N==1:
    print(-1)
else:
    import math
    if int(math.sqrt(N))**2==N:
        p=get_sieve_of_eratosthenes_new(N+1)
    else:
        p=get_sieve_of_eratosthenes_new(N)
    n=len(p)

    dp=[-10**10 for i in range(0,N+1)]

    dp[N-2]=1
    for i in range(1,n):
        for j in range(0,N-p[i]):
            dp[j]=max(dp[j],1+dp[j+p[i]])
        dp[N-p[i]]=max(1,dp[N-p[i]])

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