n = int(input())
a = list(map(int,input().split()))
ans = 0
i = 0
cnt = 0
while i <= n-2:
    if a[i] == 1 and a[i+1] == 0:
        if i == n-2:
            cnt += 1
        else:
            cnt +=2
        ans += cnt
        i += 2
    else:
        if a[i] == 1:
            ans += 1 + cnt//2
        cnt = 0
        i += 1
#     print(ans)
print(ans)