N = int(input())

if N == 1:
    
    print(-1)
    
else:
    
    isprime = [0] + [0] + [1] * (N - 1)
    
    for i in range(2, int(N ** 0.5) + 1):
        
        if isprime[i]:
            
            for j in range(2 * i, N + 1, i):
                
                isprime[j] = 0
                
    P = [i for i in range(2, N + 1) if isprime[i]]
    
    dp = [0] + [-1] * N
    
    
    for p in P:
        
        for i in range(N, p - 1, -1):
            
            if dp[i - p] != -1:
                dp[i] = max(dp[i - p] + 1, dp[i])

    print(dp[-1])