dlina = int(input())
massiv = input().split()
deystviy = 0

for i in range(dlina):
    tempDeyst = 0
    idlapoiskaed = 0
    for kjkjjljdfg in range(dlina):
        if massiv[idlapoiskaed] == '1':
            break
        idlapoiskaed += 1
    if massiv[i] == "0":
        for j in range(i):
            if massiv[j] == "1":
                tempDeyst += 1
        deystviy += tempDeyst
        massiv[i], massiv[idlapoiskaed] = massiv[idlapoiskaed], massiv[i]

print(deystviy)