[백준] 3213 피자

N = int(input())
arr = [0]*(N+1)
cnt = 0

for i in range(N) :
    x = input()
    if x=="1/4" : arr[1]+=1
    elif x=="1/2" : arr[2]+=1
    else : arr[3]+=1

while sum(arr)!=0 :
    pizza = 4
    
    for i in range(N,-1,-1) :
        while arr[i]>0 and pizza - i>=0 :
            arr[i]-=1
            pizza-=i
    cnt+=1
print(cnt)