using System;
using System.Collections.Generic;

namespace test
{
    static class Program
    {
        static void Main()
        {
            long n = long.Parse(Console.ReadLine());
            string[] astr = Console.ReadLine().Split(' ');
            long[] a = new long[n];
            for(int i = 0; i < n; i++)
            {
                a[i] = long.Parse(astr[i]);
            }
            long l = 0;
            long r = 0;
            long kosuu = 0;
            while (true)
            {
                if(l == a.Length)
                {
                    break;
                }
                if (l == r)
                {
                    if (l == a.Length - 1)
                    {
                        break;
                    }
                    else
                    {
                        if (a[l] + 1 == a[l + 1])
                        {
                            r++;
                        }
                        else
                        {
                            l++;
                            r++;
                        }
                    }
                }
                else
                {
                    if (r+1 < a.Length && a[r] + 1 == a[r + 1])
                    {
                        r++;
                    }
                    else
                    {
                        kosuu += (r - l+1) * (r - l ) / 2;
                        if(r == a.Length)
                        {
                            break; 
                        }
                        l = r+1;
                        r = l;
                    }
                }
            }
            Console.WriteLine(kosuu);
        }
    }
}