#include <iostream>
#include <fstream>
using namespace std;

long long n , x[1000005] , cont , poz;

int main ()
{
	ifstream f ("operatii.in");
	ofstream g ("operatii.out");
	
	f >> n;
	
	for (long long i = 1 ; i <= n ; ++i)
		f >> x[i];
	
	int ok2 = 1;
	while (ok2 == 1)
	{
		ok2 = 0;
		for (long long  i = 1 ; i <= n ; ++i)
		{
			if (x[i] > 0)
			{
				ok2 = 1;
				poz = i;
				while (x[poz] > 0)
					poz++;
			
				poz--;
		
				for (long long j = i ; j <= poz ; ++j)
					x[j]--;
						
				cont++;
				long long nr = poz - i;
				i += nr;
			}
			
		}
	}
	
	g << cont;
	
	return 0;
}