#include<iostream>
using namespace std;
int main()
{
	int N;
	cin >> N;
	int elavator[5005] = {};
	elavator[0] = 1;
	for(int i = 1; i <= N; i++)
	{
		cin >> elavator[i];
	}

	int price = 0;
	for(int i = 1; i <= N; i++)
	{
		if(elavator[i] > elavator[i-1])
		{
			price += (elavator[i] - elavator[i-1])*3;
		}
		else 
		{
			price += (elavator[i-1] - elavator[i])*2;
		}
	}
	cout << price << endl;

}