#include<fstream>
#include<stdio.h>
using namespace std;

int main()
{fstream f("operatii.in",ios::in);
fstream g("operatii.out",ios::out);
unsigned long n,max,val,afisare=0;

f>>n;
f>>val;
if(val)
 max=val;
else
 max=0;
for(int i=2;i<n;i++)
 {f>>val;
  if(val&&max<val)
    max=val;
  if(val==0)
   {afisare=afisare+max;
    max=0;
   }
 }
f>>val;
if(val>max)
 max=val;
afisare=afisare+max;


g<<afisare;
g.close();
f.close();
return 0;
}