#include <stdio.h>
int nr,n,maxim;
int counter;
int main()
{
    freopen ("operatii.in","r",stdin);
    freopen ("operatii.out","w",stdout);
    scanf("%d",&n);
    for(int i=1;i<=n;i++)
    {
            scanf("%d",&nr);
            if(nr!=0)
            {
                     if(maxim<nr) maxim=nr;
            }
            else
            {
                counter+=maxim;
                maxim=0;
            }
    }
    counter+=maxim;
    printf("%d\n",counter);
}