using System;
using System.Linq;
using System.Collections.Generic;

class No693{
    static void Main(){
        var a=Int32.Parse(Console.ReadLine());
        var b=Console.ReadLine().Split(' ').Select(x=>Int32.Parse(x)).OrderBy(x=>x).ToArray();
        var c=0;
        for(int i=0;i<a-1;++i){
            if(b[i]>=b[i+1]){
                c+=b[i]+1-b[i+1];
                b[i+1]=b[i]+1;
            }else if(b[i]+1<b[i+1]&&i>=a-3){
                if(b[i+1]==b[i+2]){
                    c++;
                    b[i+1]--;
                }
            }
        }
        Console.WriteLine(c);
    }
}