source_code: import java.io.OutputStream;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.PrintWriter;
  import java.util.Map;
  import java.util.Scanner;
  import java.math.BigInteger;
  import java.util.HashMap;
  
  /**
   * Built using CHelper plug-in
   * Actual solution is at the top
   *
   * @author ZYCSwing
   */
  public class Main {
      public static void main(String[] args) {
          InputStream inputStream = System.in;
          OutputStream outputStream = System.out;
          Scanner in = new Scanner(inputStream);
          PrintWriter out = new PrintWriter(outputStream);
          TaskD solver = new TaskD();
          solver.solve(1, in, out);
          out.close();
      }
  
      static class TaskD {
          public void solve(int testNumber, Scanner in, PrintWriter out) {
              int n = in.nextInt();
              int[] a = new int[n];
  
              BigInteger sum = new BigInteger("0");
              for (int i = 0; i < n; ++i) {
                  a[i] = in.nextInt();
                  long tmp = ((long) (2 * i + 1 - n)) * a[i];
                  sum = sum.add(BigInteger.valueOf(tmp));
              }
  
              Map<Integer, Integer> cnt = new HashMap<>();
  
              for (int i = n - 1; i >= 0; --i) {
                  if (cnt.containsKey(a[i] + 1)) {
                      sum = sum.subtract(BigInteger.valueOf(cnt.get(a[i] + 1)));
                  }
                  if (cnt.containsKey(a[i] - 1)) {
                      sum = sum.add(BigInteger.valueOf(cnt.get(a[i] - 1)));
                  }
                  if (cnt.containsKey(a[i])) {
                      cnt.put(a[i], cnt.get(a[i]) + 1);
                  } else {
                      cnt.put(a[i], 1);
                  }
              }
  
              out.println(sum);
          }
  
      }
  }
  
  