def seachPrimeNum(N):
    max = int(N ** 0.5)
    seachList = [i for i in range(2, N + 1)]
    primeNum = []
    while seachList[0] <= max:
        primeNum.append(seachList[0])
        tmp = seachList[0]
        seachList = [i for i in seachList if i % tmp != 0]
    primeNum.extend(seachList)
    return primeNum

N = int(input())
if N == 1:
    print(-1)
    exit()

PL = seachPrimeNum(N)
X = [0] * (N + 1)
Q = {0}
for p in PL:
    for q in sorted(list(Q),reverse = True):
        if p + q > N:
            continue
        X[p + q] = max(X[p + q], X[q] + 1)
        Q.add(p + q)

if X[N] > 0:
    print(X[N])
else:
    print(-1)