using System; using System.Collections.Generic; using System.Globalization; using System.IO; using System.Linq; partial class Solver { public void Run() { var N = ni(); long ans = 0; long lower = 2, upper = N; long left = 1, right = 1; while (lower <= upper) { // bigger for (int i = 0; i < 2 && lower <= upper; i++) { if (left > right) { ans += right * upper; right = upper; } else { ans += left * upper; left = upper; } upper--; } // smaller for (int i = 0; i < 2 && lower <= upper; i++) { if (left < right) { ans += right * lower; right = lower; } else { ans += left * lower; left = lower; } lower++; } } ans += left * right; cout.WriteLine(ans); } } // PREWRITEN CODE BEGINS FROM HERE partial class Solver : Scanner { public static void Main(string[] args) { new Solver(Console.In, Console.Out).Run(); } TextReader cin; TextWriter cout; public Solver(TextReader reader, TextWriter writer) : base(reader) { this.cin = reader; this.cout = writer; } public Solver(string input, TextWriter writer) : this(new StringReader(input), writer) { } public int ni() { return NextInt(); } public int[] ni(int n) { return NextIntArray(n); } public long nl() { return NextLong(); } public long[] nl(int n) { return NextLongArray(n); } public double nd() { return NextDouble(); } public string ns() { return Next(); } } public class Scanner { private TextReader Reader; private Queue TokenQueue = new Queue(); private CultureInfo ci = CultureInfo.InvariantCulture; public Scanner() : this(Console.In) { } public Scanner(TextReader reader) { this.Reader = reader; } public int NextInt() { return Int32.Parse(Next(), ci); } public long NextLong() { return Int64.Parse(Next(), ci); } public double NextDouble() { return double.Parse(Next(), ci); } public string[] NextArray(int size) { var array = new string[size]; for (int i = 0; i < size; i++) array[i] = Next(); return array; } public int[] NextIntArray(int size) { var array = new int[size]; for (int i = 0; i < size; i++) array[i] = NextInt(); return array; } public long[] NextLongArray(int size) { var array = new long[size]; for (int i = 0; i < size; i++) array[i] = NextLong(); return array; } public String Next() { if (TokenQueue.Count == 0) { if (!StockTokens()) throw new InvalidOperationException(); } return TokenQueue.Dequeue(); } public bool HasNext() { if (TokenQueue.Count > 0) return true; return StockTokens(); } private bool StockTokens() { while (true) { var line = Reader.ReadLine(); if (line == null) return false; var tokens = line.Trim().Split(" ".ToCharArray(), StringSplitOptions.RemoveEmptyEntries); if (tokens.Length == 0) continue; foreach (var token in tokens) TokenQueue.Enqueue(token); return true; } } }