#include<stdio.h>
FILE *f=fopen("operatii.in","r"),
     *g=fopen("operatii.out","w");
int a[1000001],i,max,op,n;
int main()
{ fscanf(f,"%d",&n);
  for(i=1;i<=n;i++) fscanf(f,"%d",&a[i]);
  i=1;
  while(i<=n) { while(a[i]==0) i++;
                while(a[i]>0) { if(a[i]>=max) { max=a[i];
                                               i++;
                                              }
                               else break;
                              }
                while(a[i]>0&&a[i]<max) i++;
                op+=max-a[i-1];
                max=0;
              }
  fprintf(g,"%d\n",op);
  fclose(f);
  fclose(g);
  return 0;
}