N=int(input())
A=[-1]+list(map(int,input().split()))

T=[0]*(N+1)

for x in range(N,0,-1):
    if x==N:
        T[N]=N
        continue
    elif x==N-1:
        if A[N-1]==1:
            T[N-1]=N
        else:
            T[N-1]=N-1
        continue
    if A[x]==0:
        T[x]=x
    else:
        if A[x+1]==1:
            T[x]=x+1
        else:
            T[x]=T[x+2]

X=0
for x in range(1,N+1):
    X+=T[x]-x

print(X)