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=[[-1 for i in range(0,N+1)] for i in range(0,n)]

    dp[0][2]=1

    for i in range(1,n):
        for j in range(0,N+1):
            if j>p[i] and dp[i-1][j-p[i]]!=-1:
                dp[i][j]=max(dp[i-1][j],1+dp[i-1][j-p[i]])
            elif j==p[i]:
                dp[i][j]=max(1,dp[i-1][j])
            else:
                dp[i][j]=dp[i-1][j]

    print(dp[n-1][N])