n = int(input())
a = input()
a = a.split()
a = list(map(int, a))
count = 0
while len(a) > 0:
    if (100 in a) and (50 in a):
        a.remove(100)
        a.remove(50)
        count += 1
    elif (100 in a):
        a.remove(100)
        count += 1
    else:
        if a.count(50) > 2:
            a.remove(50)
            a.remove(50)
            a.remove(50)
            count += 1
        elif a.count(50) == 2:
            a.remove(50)
            a.remove(50)
            count += 1
        else:
            a.remove(50)
            count += 1
print(count)