def sieve(n):
    is_prime = [True for _ in range(n+1)]
    is_prime[0] = False

    for i in range(2, n+1):
        if is_prime[i-1]:
            j = 2 * i
            while j <= n:
                is_prime[j-1] = False
                j += i
    table = [ i for i in range(1, n+1) if is_prime[i-1]]
    return table

N = int(input())
table = sieve(N)

dp = [-float('inf')] * (N + 1)
dp[0] = 0
for i in range(len(table)):
  a  = table[i]
  nxt = [-float('inf')] * (N + 1)
  for j in range(N + 1):
    nxt[j] = max(nxt[j], dp[j])
    if j + a <= N:
      nxt[j + a] = max(nxt[j + a], dp[j] + 1)
  dp = nxt
if dp[-1] < 0:
  print(-1)
else:
  print(dp[-1])