def create_prime_list(limit):
    x = limit**0.5
    primes = []
    #print('x={0}'.format(x))
    nums = [x for x in range(2, limit+1)]
    while nums[0]<=x:
        primes.append(nums[0])
        current_prime = nums[0]
        nums = [x for x in nums if x%current_prime != 0]
    primes.extend(nums)
    return primes

n = int(input())

if n == 1:
    print(-1)
    exit()

plist = create_prime_list(n)

dp = [-1]*(n+1)
dp[0] = 0

for p in plist:
    for i in range(n,-1,-1):
        if i+p <= n and dp[i] != -1:
            dp[i+p] = max(dp[i+p], dp[i]+1)
        
print(dp[n])