from random import randint, seed
seed()

n = input()

m = {3: [4], 5: [6], 7: [8,9,10,15,16,22], 11: [12], 13: [14], 19: [20,21], 23: [24,25]}

def fermat(k):
    for t in xrange(1000):
        a = randint(2, k-1)
        if pow(a, k-1, k)!=1:
            return 0
    return 1

for w in m:
    if n in m[w]:
        print w
        exit(0)

if not fermat(n-8):
    print 8
else:
    print 14