#include<stdio.h>
using namespace std;
#define dim 1000001
int v[dim];
long long s=0;
int main()
{
	int i,j,k,ok=0,operatii=0,n;
FILE *f=fopen("operatii.in","r"), *g=fopen("operatii.out","w");

fscanf(f,"%d",&n);
for(i=1;i<=n;i++)
	{
		fscanf(f,"%d",&v[i]);
		s=s+v[i];
	}

while(s!=0)
{
	for(k=1;k<=n;k++)
	{
		if(v[k]!=0)
		{	if(ok==0) i=k;
			j=k;ok=1;v[k]--;
		}
		else
		{
			if(ok==1)
				{operatii++;   s-=j-i+1;   ok=0;}
		}
	}
	
n=j;
}
fprintf(g,"%d\n",operatii);
	
	fclose(f);
	fclose(g);

return 0;}