N=int(input())
p=[True]*(N+1)
p[0]=p[1]=False
for i in range(2,N+1):
    for j in range(i*i,N+1,i):
        p[j]=False

prime=[]
for i in range(N+1):
    if p[i]:
        prime.append(i)

dp=[-1]*(N+1)
dp[0]=0

for u in prime:
    for i in range(N,-1,-1):
        if u+i<=N and dp[i]!=-1:
            dp[u+i]=max(dp[u+i],dp[i]+1)

print(dp[N])