#include<stdio.h>

int main()
{int n,v[100000],i,k,q,j;
long op,aux;
freopen("operatii.in","r",stdin);
 freopen("operatii.out","w",stdout);
 scanf("%d", &n);
 v[1]=0;
 v[n+2]=0;
 for(i=2;i<=n+1;i++)
	scanf("%d", &v[i]);
 op=0;
 aux=100;
 while(aux>0)
  {aux=0;
   k=0;
    for(i=1;i<=n+1;i++)
	 	{if ((v[i]>0)&&(v[i-1]==0)) {aux++;
		                             k=i;
		                             q=0;}
		 if((v[i]>0)&&(v[i+1]==0)) q=i;
	     if((k>0)&&(q>0)) 
		    {for(j=k;j<=q;j++)
				v[j]--;
			 k=0;
			 q=0;
			}
		}
		   
		
   
    op=op+aux;
  }
  printf("%d ",op);
  return 0;
}