import sys
input = sys.stdin.readline

N = int(input())
A = list(map(int, input().split()))
i = 0
ans = 0

while i<N:
    if A[i]==0:
        i += 1
    else:
        j = i
        
        while j<N:
            if ((j-i)%2==0 and A[j]==0) or ((j-i)%2==1 and A[j]==1):
                break
            j += 1
        
        l = j-i
        
        if j==N:
            l -= 1
        
        for k in range(l, -1, -2):
            ans += k

        i = j

print(ans)