N=int(input())
if N==1:
    print(-1)
    exit()
def eratosthenes(n):
    if n==2:
        return [2]
    prime = [2]
    limit = int(n**0.5)
    data = [i + 1 for i in range(2, n, 2)]
    while True:
        p = data[0]#まだ残ってる中での最小の素数
        if limit <= p:
            return prime + data
        prime.append(p)
        data = [e for e in data if e % p != 0]#リスト内包表記で消してる
prime=eratosthenes(N)
dp=[-1]*(N+1)
dp[0]=0
for i in prime:
    for j in reversed(range(N+1)):
        if dp[j]==-1:
            continue
        if j+i<=N:
            dp[j+i]=max(dp[j+i],dp[j]+1)
print(dp[-1] if dp[-1]!=-1 else -1)