#include <fstream>

using namespace std;

int v[1000100], n, i, maxim;
long long k;
int main()
{
	ifstream f("operatii.in");
	ofstream g("operatii.out");

	f >> n;
	for (i = 1; i <= n; i++)
		f >> v[i];
	for (i = 1; i <= n; i++)
	{
		if (v[i] == 0)
		{
			k += maxim;
			maxim = 0;
		}
		else if (v[i] > maxim)
			maxim = v[i];
	}
	if (v[n] != 0)
		k += maxim;
	g << k;
	return 0;
}