using System; using System.Diagnostics; using System.Collections.Generic; using System.Linq; using Enu = System.Linq.Enumerable; class Solution { int N; void calc() { N = ri() ; long max = 0; for (long i = 0; i < N; i++) { max = Math.Max(max, (N - i + 1) * (i + 1) - 1); } Console.WriteLine(max); } static void Main(string[] args) { new Solution().calc(); } #region static int ri() { return int.Parse(Console.ReadLine()); } static int[] ria(int n) { if (n <= 0) { Console.ReadLine(); return new int[0]; } else return Console.ReadLine().Trim().Split(' ').Select(int.Parse).ToArray(); } static void rio(out int p1) { p1 = ri(); } static void rio(out int p1, out int p2) { var r = ria(2); p1 = r[0]; p2 = r[1]; } static void rio(out int p1, out int p2, out int p3) { var r = ria(3); p1 = r[0]; p2 = r[1]; p3 = r[2]; } static void rio(out int p1, out int p2, out int p3, out int p4) { var r = ria(4); p1 = r[0]; p2 = r[1]; p3 = r[2]; p4 = r[3]; } static void rio(out int p1, out int p2, out int p3, out int p4, out int p5) { var r = ria(5); p1 = r[0]; p2 = r[1]; p3 = r[2]; p4 = r[3]; p5 = r[4]; } static long rl() { return long.Parse(Console.ReadLine()); } static long[] rla(int n) { if (n <= 0) { Console.ReadLine(); return new long[0]; } else return Console.ReadLine().Trim().Split(' ').Select(long.Parse).ToArray(); } static void rlo(out long p1) { p1 = rl(); } static void rlo(out long p1, out long p2) { var r = rla(2); p1 = r[0]; p2 = r[1]; } static void rlo(out long p1, out long p2, out long p3) { var r = rla(3); p1 = r[0]; p2 = r[1]; p3 = r[2]; } static void rlo(out long p1, out long p2, out long p3, out long p4) { var r = rla(4); p1 = r[0]; p2 = r[1]; p3 = r[2]; p4 = r[3]; } static void rlo(out long p1, out long p2, out long p3, out long p4, out long p5) { var r = rla(5); p1 = r[0]; p2 = r[1]; p3 = r[2]; p4 = r[3]; p5 = r[4]; } static double rd() { return double.Parse(Console.ReadLine()); } static double[] rda(int n) { if (n <= 0) { Console.ReadLine(); return new double[0]; } else return Console.ReadLine().Trim().Split(' ').Select(double.Parse).ToArray(); } static void rdo(out double p1) { p1 = rd(); } static void rdo(out double p1, out double p2) { var r = rda(2); p1 = r[0]; p2 = r[1]; } static void rdo(out double p1, out double p2, out double p3) { var r = rda(3); p1 = r[0]; p2 = r[1]; p3 = r[2]; } static void rdo(out double p1, out double p2, out double p3, out double p4) { var r = rda(4); p1 = r[0]; p2 = r[1]; p3 = r[2]; p4 = r[3]; } static void rdo(out double p1, out double p2, out double p3, out double p4, out double p5) { var r = rda(5); p1 = r[0]; p2 = r[1]; p3 = r[2]; p4 = r[3]; p5 = r[4]; } static void swap(ref T x, ref T y) { T temp = x; x = y; y = temp; } static void wa1(T[] a) { Debug.WriteLine(string.Join(" ", a)); } static void wa2(T[][] a) { foreach (var row in a) { Debug.WriteLine(String.Join(" ", row)); } } [DebuggerDisplay("{x} , {y}")] class point { public int x, y; public point(int x, int y) { this.x = x; this.y = y; } } #endregion } static class Extention { public static T[][] ToJagArray(this T[,] a) { int n = a.GetLength(0), m = a.GetLength(1); var ret = new T[n][]; for (int i = 0; i < n; i++) { ret[i] = new T[m]; for (int j = 0; j < m; j++) { ret[i][j] = a[i, j]; } } return ret; } }