ans.java

import java.io.*;
import java.util.*;
// Bhava nahi aathavt java try kar
public class Main {

  public static void main(String[] args) throws Exception {
    // write your code here
    Scanner scn = new Scanner(System.in);

    int n1 = scn.nextInt();
    int arr1[] = new int[n1];
    for (int i = 0; i < arr1.length; i++) {
      arr1[i] = scn.nextInt();
    }

    int  arr2[] = {}
    for (int i = 0; i < arr1.length; i++) {
      if (i == 0) {
        arr2.push(arr[0]);
      }
      if (i ==  1) {
        int sub = arr[1] - arr[0];
        // console.log(sub);
        arr2.push(sub);
      }
      if (i == 2) {
        arr2.push(0);
      }
      if (i == 3) {
        int sub2 = arr[3] - arr[2];
        arr2.push(sub);
      }
    }
    int sum = 0;
    for (int i = 0; i < arr2.length; i++) {
      sum += arr[i];

    }
    System.out.println(sum)
  }

}