#include<fstream>
#include<algorithm>
#include<vector>
using namespace std;

int n,v[1000005];

int main()
{
	ifstream f("operatii.in");
	ofstream g("operatii.out");
	f>>n;
	int start,contor=0,finish,i,maxim=0;
	start=0;
	for(i=1;i<=n+1;i++)
	{
		f>>v[i];
		if(v[i]!=0&&start==0)
			start=i;
		if(v[i]>maxim)
			maxim=v[i];
		if(v[i]==0&&start!=0)
		{
			finish=i-1;
		
		contor=contor+maxim;
		maxim=0;
		start=0;
		}
	}
	g<<contor;
	f.close();
	g.close();
	return 0;
}