using static System.Math;
using System;

public class Hello
{
    static void Main()
    {
        var n = int.Parse(Console.ReadLine().Trim());
        string[] line = Console.ReadLine().Trim().Split(' ');
        var p = Array.ConvertAll(line, int.Parse);
        getAns(n, p);
    }
    static void getAns(int n, int[] p)
    {
        if (n == 1) { Console.WriteLine(0); return; }
        var ans = n * (n + 1) / 2L;
        var pp = 0;
        for (int i = 0; i < n; i++)
        {
            if (p[i] == n) { pp = i + 1; break; }
        }
        ans -= 2L * pp;
        Console.WriteLine(Max(0, ans));
    }
}