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) for _ in range(len(plist))]

for i,p in enumerate(plist):
    dp[i][p] = 1

for i in range(len(plist)):
    for S in range(1,n+1):
        if dp[i-1][S] >= 1:
            dp[i][S] = max(dp[i-1][S], dp[i][S])
        elif S-plist[i] >= 0 and dp[i-1][S-plist[i]] >= 1:
            dp[i][S] = max(dp[i-1][S-plist[i]]+1, dp[i][S])

print(dp[len(plist)-1][n])