source_code: import java.io.OutputStream;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.PrintWriter;
  import java.util.StringTokenizer;
  import java.util.HashMap;
  import java.math.BigInteger;
  import java.io.IOException;
  import java.io.BufferedReader;
  import java.io.InputStreamReader;
  import java.io.InputStream;
  
  /**
   * Built using CHelper plug-in
   * Actual solution is at the top
   *
   * @author Liavontsi Brechka
   */
  public class Main {
      public static void main(String[] args) {
          InputStream inputStream = System.in;
          OutputStream outputStream = System.out;
          InputReader in = new InputReader(inputStream);
          PrintWriter out = new PrintWriter(outputStream);
          TaskD solver = new TaskD();
          solver.solve(1, in, out);
          out.close();
      }
  
      static
      @SuppressWarnings("Duplicates")
      class TaskD {
          public void solve(int testNumber, InputReader in, PrintWriter out) {
              int n = in.nextInt();
              long[] a = in.nextLongArray(n);
              HashMap<Integer, Integer> count = new HashMap<>();
  
              BigInteger res = BigInteger.ZERO;
              long prev = 0;
              count.put((int) a[0], 1);
  
              long temp;
              long nextRes;
              for (int i = 1; i < n; i++) {
                  temp = ((a[i] - a[i - 1]) * i + prev);
                  nextRes = temp - count.getOrDefault((int) a[i] - 1, 0) + count.getOrDefault((int) a[i] + 1, 0);
                  res = res.add(new BigInteger(String.valueOf(nextRes)));
                  count.put((int) a[i], count.getOrDefault((int) a[i], 0) + 1);
                  prev = temp;
              }
  
              out.print(res);
          }
  
      }
  
      static class InputReader {
          private final BufferedReader reader;
          private StringTokenizer tokenizer;
  
          public InputReader(InputStream in) {
              reader = new BufferedReader(new InputStreamReader(in));
          }
  
          public long[] nextLongArray(int size) {
              long[] array = new long[size];
              for (int i = 0; i < size; ++i) {
                  array[i] = nextLong();
              }
              return array;
          }
  
          public int nextInt() {
              return Integer.parseInt(next());
          }
  
          public long nextLong() {
              return Long.parseLong(next());
          }
  
          public String next() {
              while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                  tokenizer = new StringTokenizer(readLine());
              }
              return tokenizer.nextToken();
          }
  
          public String readLine() {
              String line;
              try {
                  line = reader.readLine();
              } catch (IOException e) {
                  throw new RuntimeException(e);
              }
              return line;
          }
  
      }
  }
  
  