n=int(input())
l=list(map(int,input().split()))
c=0
nl=[]
for i in l:
    if i==1:
        nl.append(0)
    else:
        nl.append(1)
ml=l
d=0
K=[]
for i in range(n):
    if l[i]==1:
        K.append(i)
for j in K:
    for i in range(n-1):
        if l[j+i]==1 and j+i<n-1:
            c+=1
            if c%2==1:
                l=nl
            else:
                l=ml
        else:
            d+=c
            c=0
            l=ml
            break
print(d)