#include<fstream.h>
long a[320],max,n,v[320];
int poz,k,i,j,op,aux[50],x,ok;
int main ()
{
ifstream f("operatii.in");
ofstream g("operatii.out");
f>>n;
for (i=0;i<n;i++) {f>>a[i];
			if (max<a[i]) max=a[i];}
ok=1;
while (ok)
	{for (i=0;i<n;i++)
		if (a[i]==max)
			{poz=i;a[poz]--;
			 while (a[poz+1]==max)
				{a[poz+1]--;poz++;}
			 op++;}
	 max=0;
	 for (i=0;i<n;i++)
		if (max<a[i]) max=a[i];
	 if (max==0) ok=0;}
g<<op;
return 0;
}