N =int(input())
p=[2];A=N
for i in range(3,A):
    s=True
    for j in p:
        if i%j == 0:s=False
    if s==True:p.append(i)

lis =[0]*(N+1)
for pr in p:
    for i in range(N-pr+1):
        if lis[(N-i)-pr]!=0 or N-i-pr ==0:
            lis[N-i] =max(lis[N-i],lis[N-i-pr]+1)
        else:
            lis[N-i] = lis[N-i]
if lis[N] ==0:
    print(-1)
else:
    print(lis[N])