Squirrel Liss loves nuts. There are n trees (numbered 1 to n from west to east) along a street and there is a delicious nut on the top of each tree. The height of the tree i is hi. Liss wants to eat all nuts.

Now Liss is on the root of the tree with the number 1. In one second Liss can perform one of the following actions:

  * Walk up or down one unit on a tree. 
  * Eat a nut on the top of the current tree. 
  * Jump to the next tree. In this action the height of Liss doesn't change. More formally, when Liss is at height h of the tree i (1 ≤ i ≤ n - 1), she jumps to height h of the tree i + 1. This action can't be performed if h > hi + 1. 



Compute the minimal time (in seconds) required to eat all nuts.

Input

The first line contains an integer n (1 ≤ n ≤ 105) — the number of trees.

Next n lines contains the height of trees: i-th line contains an integer hi (1 ≤ hi ≤ 104) — the height of the tree with the number i.

Output

Print a single integer — the minimal time required to eat all nuts in seconds.

Examples

Input

2
1
2


Output

5


Input

5
2
1
2
1
1


Output

14
import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.StringTokenizer;


public class B {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		Parser p = new Parser(System.in);
		PrintWriter pw = new PrintWriter(System.out);
		int n = p.nextInt();
		int[] heights = p.nextIntArray(n);
		int time = 1+heights[0];
		for(int i=0; i<n; ++i){//zjadla z itego drzewa
			if(i +1 == n){
				break;
			}
			int next = i+1;
			int dif = Math.abs(heights[next]- heights[i]);
			if(dif == 0){
				time+=2;
			}else{
				time+=dif;
				time+=2;
			}
		}
		
		pw.print(time);
		pw.close();
	}

	
	
	
	
	
	
	
	
	
	
	
	
	
	
	
	static class Parser{
		
		StringTokenizer st;
		BufferedReader br;

		public Parser(InputStream is){
			this.br = new BufferedReader( new InputStreamReader(is));
			
		}
		
		public int nextInt(){
			return Integer.parseInt(nextToken());
		}
		
		public double nextDouble(){
			return Double.parseDouble(nextToken());
		}
		
		public String nextString(){
			return nextToken();
		}
		
		public int[] nextIntArray(int s){
			int[] a = new int[s];
			for(int i=0; i<s; ++i){
				a[i] = nextInt();
			}
			return a;
		}
		
		public int[][] nextIntTable(int r, int c){
			int[][] a = new int[r][c];
			for(int i=0; i<r; ++i){
				a[i] = nextIntArray(c);
			}
			return a;
		}
	
		private String nextToken() {
			if( st == null || ! st.hasMoreTokens() ){
				try{
					st = new StringTokenizer( br.readLine());
				}catch( Exception e){
					e.printStackTrace();
				}
			}
			return st.nextToken();
		}
		
	}
}



