#include <stdio.h>
long int v[10000],n;

int gaseste (void)
     {
     long int c,s,d,i,nr=0,ok;
     ok=1;
     while (ok)
	   {
	   ok=0;
	   for (i=1;i<=n;)
	       {
	       if (v[i])
		  {
		  ok=1;
		  while (v[i])
			{
			--v[i];
			++i;
			}
		  nr++;
		  }
	       else
		  ++i;
	       }
	   }
     return nr;
     }


int main ()
 {
 long int i,x;
 FILE *f;
 f=fopen("operatii.in","r");
 fscanf(f,"%ld",&n);
 for (i=1;i<=n;i++)
     fscanf(f,"%ld",&v[i]);
 fclose(f);
 f=fopen("operatii.out","w");
 x=gaseste();
 fprintf(f,"%ld",x);
 fclose(f);
 return 0;
 }