#include<iostream>
using namespace std;
int N;
int A[2<<17];
int cnt[2<<17];
main()
{
	cin>>N;
	for(int i=0;i<N;i++)cin>>A[i];
	long ans=0;
	for(int i=N;i--;)
	{
		if(i+1<N&&A[i]==1)
		{
			if(A[i+1]==1)cnt[i]=1;
			else cnt[i]=cnt[i+2]+2;
		}
		else cnt[i]=0;
		ans+=cnt[i];
	}
	cout<<ans<<endl;
}