题解 | #素数伴侣#

import math
def check(num):
    for i in range(2,int(math.sqrt(num))+2):
        if num%i==0:
            return False
    return True
def find(odd,visited,choose,evens):
    for i,even in enumerate(evens):
        if check(odd+even) and not visited[i]:
            visited[i]=True
            if choose[i]==0 or find(choose[i],visited,choose,evens):
                choose[i]=odd
                return True
    return False

while True:
    try:
        n=input()
        li=map(int,input().split(' '))
        evens=[]
        odds=[]
        count=0
        for i in li:
            if i%2==0:
                evens.append(i)
            else:
                odds.append(i)
        choose=[0]*len(evens)
        for odd in odds:
            visited=[False]*len(evens)
            if find(odd,visited,choose,evens):
                count+=1
        print(count)
    except:
        break