#include<fstream.h>
int main()
{
long long n,i,ok1,nr,ok,a[1000001];
ifstream f("operatii.in");
ofstream g("operatii.out");
f>>n;
for (i=0;i<=n;i++)
     f>>a[i];
ok=0;
nr=0;
while (ok=0)
	{
	ok1=0;	
	for (i=0;i<=n;i++)
   	if (a[i]!=0){
		     a[i]=a[i]-1;
		     ok1=1;
		     if (a[i+1]==0)break;
		    }
        nr=nr+1;
        ok=1;
        for (i=0;i<=n;i++)
            if (a[i]!=0) {
			  ok=ok-1;
			  break;
			 }
	}
g<<nr;
f.close();
g.close();
return 0;
}