import sys
readline = sys.stdin.readline

N = int(readline())

fact = [True] * (N + 1)
fact[0] = fact[1] = False

F = []
for i in range(2, len(fact)):
  if fact[i]:
    F.append(i)
    for j in range(i * 2, len(fact), i):
      fact[j] = False
      
# 重さがそれぞれの数で、価値が1のナップサックを解く
dp = [-1] * (N + 1)
dp[0] = 0
for i in range(len(F)):
  for j in range(len(dp) - 1, -1, -1):
    if dp[j] == -1:
      continue
    if j + F[i] <= N:
      dp[j + F[i]] = max(dp[j + F[i]], dp[j] + 1)
      
print(dp[N])