n=int(input())
a=list(map(int,input().split()))
L=[-1]*(n+1)
for i in range(n):
  if a[i]==0:
    L[i]=i
L[-1]=n+1
for i in range(n-1,-1,-1):
  if L[i]==-1:
    L[i]=L[i+1]

ans=0
for i in range(n):
  ans+=max(n-L[i],0)
print(ans)