#include <stdio.h>

FILE *f,*g;

long long s,max;
long i,n,a[1000001],v[1000001];

int main()
{

 f=fopen("operatii.in","r");
 g=fopen("operatii.out","w");

 fscanf(f,"%ld", &n);
 for (i=1;i<=n;i++)
	fscanf(f,"%ld", &v[i]);
 fclose(f);
 i=1;
 while (i<n)
  {
   while (v[i]==0)
	i++;
   while (v[i]!=0)
	{
	 if (v[i]>max)
		max=v[i];
	 i++;
	}
   s+=max;
   max=0;
  }
 if (max)
	s+=max;
 fprintf(g,"%lld", s);
 fclose(g);

 return 0;
}