#include<fstream.h>
#define MAX 1000000

long n,a[MAX],op;


void citire()
{
	ifstream fin("operatii.in");
	long i;
	fin>>n;
	for(i=1;i<=n;i++)
		fin>>a[i];
	fin.close();
}



void numara()
{
	long i=1,j,min,k;
	while(i<=n)
		{
			while(!a[i]&&i<=n)
				i++;
			j=i;
			min=a[i];
			while(a[j])
				{
					if(a[j]<min) min=a[j];
					j++;
				}
			op+=min;
			for(k=i;k<j;k++)
				a[k]-=min;
		}
}


void afis()
{
	ofstream fout("operatii.out");
	fout<<op<<'\n';
	fout.close();
}


int main()
{
	citire();
	numara();
	afis();
	return 0;
}