import sys


def input(): return sys.stdin.readline().rstrip('\n')


def isp(x):
    if x < 2:
        return False
    i = 2
    while i*i <= x:
        if x % i == 0:
            return False
        i += 1
    return True


def main():
    n = int(input())
    d = [0] + [-float('inf')]*n
    for i in range(1, n+1):
        if isp(i):
            for j in range(n, i-1, -1):
                d[j] = max(d[j], d[j-i]+1)

    print(max(-1, d[n]))


if __name__ == '__main__':
    main()