N = int(input())

def dpsum(N):
    if N == 1:
        return -1
    pn = [2]
    for i in range(3,N+1,2):
        for s in pn:
            if i%s == 0:break
        else:pn += [i]
    Q = [1]+[0]*N
    for p in pn:
        for i in range(N,-1,-1):
            if Q[i] > 0 and i+p <= N:
                Q[i+p] = max(Q[i+p], Q[i]+1)
    return Q[N]-1

print(dpsum(N))