n = int(input())

prime = [True for _ in range(n + 1)]
prime[0] = False
prime[1] = False
for x in range(2, n + 1):
  if not prime[x]:
    continue
  for y in range(2 * x, n + 1, x):
    prime[y] = False

dp = [None for _ in range(n + 1)]
dp[0] = 0
for x in range(2, n + 1):
  if not prime[x]:
    continue
  for y in range(n - x, -1, -1):
    if dp[y] is None:
      continue
    if dp[y + x] is None:
      dp[y + x] = dp[y] + 1
    else:
      dp[y + x] = max(dp[y + x], dp[y] + 1)

if dp[n] is None:
  print("-1")
else:
  print(dp[n])