using System; using System.Linq; using System.Linq.Expressions; using System.Collections.Generic; using Debug = System.Diagnostics.Debug; using StringBuilder = System.Text.StringBuilder; using System.Numerics; using Point = System.Numerics.Complex; using Number = System.Int64; namespace Program { public class Solver { public void Solve() { var n = sc.Integer(); var k = sc.Long(); var a = sc.Integer(n); var P = new FactorialNumber(a); Debug.WriteLine(P); var i1 = P.GetInversion(); var m = P.Add(k); var i2 = P.GetInversion(); Debug.WriteLine(P); IO.Printer.Out.WriteLine(m * FactorialNumber.fact[n] * n * (n - 1) * ModInteger.Inverse(4) + i2 - i1); } public IO.StreamScanner sc = new IO.StreamScanner(Console.OpenStandardInput()); static T[] Enumerate(int n, Func f) { var a = new T[n]; for (int i = 0; i < n; ++i) a[i] = f(i); return a; } static public void Swap(ref T a, ref T b) { var tmp = a; a = b; b = tmp; } } } #region main static class Ex { static public string AsString(this IEnumerable ie) { return new string(System.Linq.Enumerable.ToArray(ie)); } static public string AsJoinedString(this IEnumerable ie, string st = " ") { return string.Join(st, ie); } static public void Main() { var solver = new Program.Solver(); solver.Solve(); Program.IO.Printer.Out.Flush(); } } #endregion #region Ex namespace Program.IO { using System.IO; using System.Text; using System.Globalization; public class Printer : StreamWriter { static Printer() { Out = new Printer(Console.OpenStandardOutput()) { AutoFlush = false }; } public static Printer Out { get; set; } public override IFormatProvider FormatProvider { get { return CultureInfo.InvariantCulture; } } public Printer(System.IO.Stream stream) : base(stream, new UTF8Encoding(false, true)) { } public Printer(System.IO.Stream stream, Encoding encoding) : base(stream, encoding) { } public void Write(string format, T[] source) { base.Write(format, source.OfType().ToArray()); } public void WriteLine(string format, T[] source) { base.WriteLine(format, source.OfType().ToArray()); } } public class StreamScanner { public StreamScanner(Stream stream) { str = stream; } public readonly Stream str; private readonly byte[] buf = new byte[1024]; private int len, ptr; public bool isEof = false; public bool IsEndOfStream { get { return isEof; } } private byte read() { if (isEof) return 0; if (ptr >= len) { ptr = 0; if ((len = str.Read(buf, 0, 1024)) <= 0) { isEof = true; return 0; } } return buf[ptr++]; } public char Char() { byte b = 0; do b = read(); while ((b < 33 || 126 < b) && !isEof); return (char)b; } public string Scan() { var sb = new StringBuilder(); for (var b = Char(); b >= 33 && b <= 126; b = (char)read()) sb.Append(b); return sb.ToString(); } public string ScanLine() { var sb = new StringBuilder(); for (var b = Char(); b != '\n'; b = (char)read()) if (b == 0) break; else if (b != '\r') sb.Append(b); return sb.ToString(); } public long Long() { if (isEof) return long.MinValue; long ret = 0; byte b = 0; var ng = false; do b = read(); while (b != 0 && b != '-' && (b < '0' || '9' < b)); if (b == 0) return long.MinValue; if (b == '-') { ng = true; b = read(); } for (; true; b = read()) { if (b < '0' || '9' < b) return ng ? -ret : ret; else ret = ret * 10 + b - '0'; } } public int Integer() { return (isEof) ? int.MinValue : (int)Long(); } public double Double() { var s = Scan(); return s != "" ? double.Parse(s, CultureInfo.InvariantCulture) : double.NaN; } private T[] enumerate(int n, Func f) { var a = new T[n]; for (int i = 0; i < n; ++i) a[i] = f(); return a; } public char[] Char(int n) { return enumerate(n, Char); } public string[] Scan(int n) { return enumerate(n, Scan); } public double[] Double(int n) { return enumerate(n, Double); } public int[] Integer(int n) { return enumerate(n, Integer); } public long[] Long(int n) { return enumerate(n, Long); } } } #endregion #region ModNumber public partial struct ModInteger { public const long Mod = (long)1e9 + 7; public long num; public ModInteger(long n) : this() { num = n % Mod; if (num < 0) num += Mod; } public override string ToString() { return num.ToString(); } public static ModInteger operator +(ModInteger l, ModInteger r) { var n = l.num + r.num; if (n >= Mod) n -= Mod; return new ModInteger() { num = n }; } public static ModInteger operator -(ModInteger l, ModInteger r) { var n = l.num + Mod - r.num; if (n >= Mod) n -= Mod; return new ModInteger() { num = n }; } public static ModInteger operator *(ModInteger l, ModInteger r) { return new ModInteger(l.num * r.num); } public static ModInteger operator ^(ModInteger l, long r) { return ModInteger.Pow(l, r); } public static implicit operator ModInteger(long n) { return new ModInteger(n); } public static ModInteger Pow(ModInteger v, long k) { ModInteger ret = 1; var n = k; for (; n > 0; n >>= 1, v *= v) { if ((n & 1) == 1) ret = ret * v; } return ret; } } #endregion #region Inverse public partial struct ModInteger { static public ModInteger Inverse(ModInteger v) { long p, q; ExGCD(v.num, Mod, out p, out q); return new ModInteger(p % Mod + Mod); } static public long ExGCD(long a, long b, out long x, out long y) { var u = new long[] { a, 1, 0 }; var v = new long[] { b, 0, 1 }; while (v[0] != 0) { var t = u[0] / v[0]; for (int i = 0; i < 3; i++) { var tmp = u[i] - t * v[i]; u[i] = v[i]; v[i] = tmp; } } x = u[1]; y = u[2]; if (u[0] > 0) return u[0]; for (int i = 0; i < 3; i++) u[i] = -u[i]; return u[0]; } } #endregion #region FNS public partial class FactorialNumber { int n; int[] a; public FactorialNumber(int[] perm) { n = perm.Length; var bit = new fenwickTree(n); a = new int[n]; for (int i = n - 1; i >= 0; i--) { var x = perm[i]; a[i] = bit[x]; bit.Add(x, 1); } } public long Add(long k) { for (int i = 0; i < n; i++) { var t = k + a[n - 1 - i]; a[n - 1 - i] = (int)(t % (i + 1)); k = t / (i + 1); } return k; } public override string ToString() { return string.Join(" ", a); } #region FenwickTree [System.Diagnostics.DebuggerDisplay("Data={ToString()}")] public class fenwickTree { int n; int[] bit; int max = 1; public fenwickTree(int size) { n = size; bit = new int[n + 1]; while ((max << 1) <= n) max <<= 1; } /// sum[a,b] public int this[int i, int j] { get { return this[j] - this[i - 1]; } } /// sum[0,i] public int this[int i] { get { int s = 0; for (; i > 0; i -= i & -i) s += bit[i]; return s; } } public int LowerBound(int w) { if (w <= 0) return 0; int x = 0; for (int k = max; k > 0; k >>= 1) if (x + k <= n && bit[x + k] < w) { w -= bit[x + k]; x += k; } return x + 1; } /// add v to bit[i] public void Add(int i, int v) { if (i == 0) System.Diagnostics.Debug.Fail("BIT is 1 indexed"); for (; i <= n; i += i & -i) bit[i] += v; } public override string ToString() { return string.Join(",", Enumerable.Range(0, n + 1).Select(i => this[i, i])); } } #endregion } #endregion #region FNS Inversion public partial class FactorialNumber { const int MN = 100050; static public ModInteger[] fact; static void Build() { fact = new ModInteger[MN]; fact[0] = 1; for (int i = 1; i < MN; i++) fact[i] = i * fact[i - 1]; } public ModInteger GetInversion() { if (fact == null) Build(); ModInteger ret = 0; ModInteger v = 0; ModInteger f = 1; for (int i = n - 1; i >= 0; i--) { var k = n - 1 - i; ret += a[i] * fact[k] * k * (k - 1) * ModInteger.Inverse(4); ret += f * (a[i] * (a[i] - 1)) * ModInteger.Inverse(2); ret += a[i] * v; v += a[i] * f; f *= n - i; } return ret; } } #endregion