using System; using static System.Console; using System.Linq; using System.Collections.Generic; class Program { static int NN => int.Parse(ReadLine()); static int[] NMi => ReadLine().Split().Select(c => int.Parse(c) - 1).ToArray(); static int[][] NMap(int n) => Enumerable.Repeat(0, n).Select(_ => NMi).ToArray(); public static void Main() { Solve(); } static void Solve() { var n = NN; var m = (n + 1L) / 2; WriteLine(m * (m + 1) / 2); } }