#include<fstream>
#include<algorithm>
 
using namespace std;
  
long long n,v[1000005],contor=0,maxim=0,start;
  
int main()
{
    ifstream f("operatii.in");
    ofstream g("operatii.out");
    f>>n;
     
         int i;
    for(i=1;i<=n;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)
        {       
         contor=contor+maxim;
        maxim=0;
        start=0;
        }
    }
    g<<contor;
    f.close();
    g.close();
    return 0;
}