#include<fstream.h>
int v[1000001];
int main()
{
	int n,i,k=0,ok,j;
	ifstream f("operatii.in");
	ofstream g("operatii.out");
	f>>n;
	for (i=1;i<=n;i++)
		f>>v[i];
	do
	{
		j=1;
		ok=1;
		while (v[j]==0)
		{
			j++;
			if (j==n+1) {ok=0;break;}
		}
		if (ok==0) break;
		for (i=j;i<=n+1;i++)
		{
			if (v[i]!=0) v[i]--;
			else if (v[i]==0){k++;break;}
		}
	}
	while (ok==1);
	g<<k;
	return 0;
}