#include<stdio.h>)

int main()
{int n,v[10000],i,aux,op,k,q,j;
 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]--;}
		   
		}
   
    op=op+aux;
  }
  printf("%d", op+1);
  return 0;
}