#include <iostream>
#include <cstdlib>
#include <cstdio>

using namespace std;

int main()
{
	 int n,i;
	 int bod[102];
	 int zbod[102];
	 int raz=0;
	 int p=0;
	 int a=1;

	 cin>>n;
	 for(i=0;i<n;i++)
		  {
			   cin>>bod[i];
		  }

	 int nbod=bod[n-1]+1;

	 for(i=(n-1);i>=0;i--)
		  {
			   
			   zbod[i]=nbod-1;
			  if(zbod[i]==bod[n-a])
			  {
					raz=raz+p;
					p--;
			  }
			  else
			  {
				   p=(bod[n-a])-zbod[i];
				   abs(p);
				   raz=raz+p;
			  }
			  a++;  
		  }

	 raz=abs(raz);

	 if(raz==n)
	 {
	 cout<<raz<<endl;
	 }
	 else
	 {cout<<raz+n<<endl;}
	 return 0;
}