#yuki1765
n=int(input())
a=list(map(int,input().split()))
cnt=0
x=0
if a[0]==1:
 x=1
for i in range(1,n):
 if a[i]!=a[i-1]:
  cnt+=x
 else:
  cnt+=x
  x=0
 if a[i]==1:
  x+=1
print(cnt)