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