#include <stdio.h>


 int a[1000001],n,nr,i,j,k,max;
 long p;

 int main()
  {FILE *fin,*fout;


  fin=fopen("operatii.in","r");
  fscanf(fin,"%d",&n);
  for (i=1;i<=n;i++)
       fscanf(fin,"%d",&a[i]);
  fclose(fin);

  p=0;
  i=1;
  while (i<=n)
    {if (a[i]!=0) {j=i;
                   max=a[i];
                   p+=max;
                   while ((a[j]!=0)&&(j<=n))
                      {if (a[j]>max) {p+=a[j]-max;
                                      max=a[j];
                                      }
                       j++;
                       }
                    i=j-1;
                    }
      i++;
      }

  fout=fopen("operatii.out","w");
  fprintf(fout,"%ld",p);
  fclose(fout);

  return 0;
  }