#include <iostream>
#include <fstream>
using namespace std;

int main()
{
	ifstream f ("operatii.in");
	ofstream g ("operatii.out");
	
	int n , x[3005] , dim , y[3005] , poz , sum = 0;
	
	f >> n;
	for (int i = 1 ; i <= n ; ++i)
		f >> x[i];
	
	for (int i = 1 ; i <= n ; ++i)
	{
		dim = 0;
		if (x[i] == 0)
		{
			poz = i + 1;
			
			while (x[poz] != 0)
				poz++;
			if(poz != i+1)
			{
				dim = 1;
				y[dim] = x[i+1];
				for (int j = i + 2 ; j < poz ; ++j)
					for (int p = 1 ; p <= dim ; ++p)
					if (y[p] != x[j])
					{
						dim++;
						y[dim] = x[j];
					}
			}
		}
			sum += dim;
				
		}
	
	g << sum;
	return 0;
}