import sys

def II(): return int(sys.stdin.readline())

def main():
    prime=[0,1]*10005
    prime[1]=0
    prime[2]=1
    for x in range(3,20001):
        if x**2>20000:break
        if prime[x]:
            for y in range(x**2,20001,x):
                prime[y]=0
    pp=[]
    for p in range(2,20001):
        if prime[p]:pp.append(p)

    cntpri=[-1]*20001
    cntpri[0]=0
    for p in pp:
        for x in range(20000,-1,-1):
            if cntpri[x]==-1:continue
            if x+p>20000:continue
            cntpri[x+p]=max(cntpri[x+p],cntpri[x]+1)
    print(cntpri[II()])

main()