#include<fstream>
using namespace std;
unsigned int n,i,j,x,max1,nrmin,ok;
int main()
{
	ifstream f("operatii.in");
	ofstream g("operatii.out");
	f>>n;
	for(i=1;i<=n;i++)
	{
		f>>x;
		if(x==0&&ok==0)
		{
			nrmin+=max1;
		max1=0;
		ok=1;
		}
		else
		{
			ok=0;
	      if(x!=0&&x>max1)
		   max1=x;
		}
	}
	nrmin+=max1;
	g<<nrmin<<"\n";
	return 0;
}