import sys
input = sys.stdin.readline

N = int(input())
As = list(map(int, input().split()))

total, value = 0, 0
target = 1

for a in As[:-1]:
    if a == 1:
        if target == 1:
            value += 1
            target = 0
        else:
            value = 1
    else:
        if target == 0:
            pass
        else:
            value = 0
        target = 1
    total += value

print(total)