source_code: import java.io.*;
  import java.math.BigInteger;
  import java.util.*;
  public class DD {
  	public static void main(String[] args)throws Throwable {
  		MyScanner sc=new MyScanner();
  		PrintWriter pw=new PrintWriter(System.out);
  		
  		int n=sc.nextInt();
  		int [] a=new int [n];
  		for(int i=0;i<n;i++)
  			a[i]=sc.nextInt();
  		
  		TreeMap<Integer, Integer> map=new TreeMap<Integer, Integer>();
  		BigInteger ans=new BigInteger("0");
  		long sum=0;
  		for(int i=0;i<n;i++){
  			sum+=a[i];
  			map.put(a[i], map.getOrDefault(a[i], 0)+1);
  			int cntSame=map.get(a[i]);
  			int cntLess=map.getOrDefault(a[i]-1, 0);
  			int cntMore=map.getOrDefault(a[i]+1, 0);
  			long sum2=sum;
  			sum2-=1L*cntSame*a[i];
  			sum2-=1L*cntLess*(a[i]-1);
  			sum2-=1L*cntMore*(a[i]+1);
  			int cnt=i+1-(cntSame+cntLess+cntMore);
  			ans = ans.subtract(BigInteger.valueOf(sum2));
  			ans= ans.add(BigInteger.valueOf(1L*cnt*a[i]));
  			
  		}
  		pw.println(ans);
  		pw.flush();
  		pw.close();
  	}
  	
  	static class MyScanner {
  		BufferedReader br;
  		StringTokenizer st;
  		public MyScanner() {
  			br = new BufferedReader(new InputStreamReader(System.in));
  		}
  		String next() {while (st == null || !st.hasMoreElements()) {
  			try {st = new StringTokenizer(br.readLine());}
  			catch (IOException e) {e.printStackTrace();}}
  		return st.nextToken();}
  		int nextInt() {return Integer.parseInt(next());}
  		long nextLong() {return Long.parseLong(next());}
  		double nextDouble() {return Double.parseDouble(next());}
  		String nextLine(){String str = "";
  		try {str = br.readLine();}
  		catch (IOException e) {e.printStackTrace();}
  		return str;}
  	}
  }