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

long long n , x[1000005] , sum;


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