Language: C++

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Diagnostics;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading.Tasks;
using System.Numerics;
using System.IO;
using System.Runtime.InteropServices;
using static System.Math;
using static Math2;
using static io;
using static Utils;



public class CompetitiveProgramming
{

  public void Solve()
  {
    var o = Longs;
    var n = o[0];
    var m = o[1];
    var d = o[2];
    if (d == 0)
    {
      Write((double)(m - 1) / (double)n);
    }
    else
    {
      double x = 2 * (m - 1) * (n - 1);
      Write(x / n / n);
    }
  }


}

public class Factorical
{
  public long[] Fact;
  public long[] invFact;
  public Factorical(long N, long MOD = 1000000007)
  {
    Fact = new long[N + 1];
    invFact = new long[N + 1];
    Fact[0] = 1;
    for (long i = 1; i <= N; ++i)
    {
      Fact[i] = Fact[i - 1] * i % MOD;
    }
    invFact[N] = Power(Fact[N], MOD - 2);
    for (long i = N; i > 0; --i)
    {
      invFact[i - 1] = invFact[i] * i % MOD;
    }
  }
  public long Comb(long n, long r, long MOD = 1000000007) => Fact[n] * invFact[r] % MOD * invFact[n - r] % MOD;
}

public static class Math2
{
  public const int INF = 1 << 29;
  public const long INFL = 1L << 60;
  public const long MOD = 1000000007;
  public const int MOD2 = 998244353;

  public static long Power(long a, long b, long MOD = 1000000007)//i^N
  {
    long res = 1;
    while (b > 0)
    {
      if ((b & 1) != 0) res = res * a % MOD;
      a = a * a % MOD;
      b >>= 1;
    }
    return res;
  }
  public static long Power2(long a, long b)//i^N
  {
    long res = 1;
    while (b > 0)
    {
      if ((b & 1) != 0) res = res * a;
      a = a * a;
      b >>= 1;
    }
    return res;
  }
  public static long GCD(long a, long b)
  {
    while (b > 0)
    {
      var r = a % b;
      a = b;
      b = r;
    }
    return a;
  }
  public static long LCM(long a, long b) => (b / GCD(a, b)) * a;
  public static long Comb(long n, long r, int MOD = 1000000007)
  {
    long ret = 1;
    long x = 1;
    for (long i = n; i >= n - r + 1; --i)
    {
      ret = ret / x * i;
      ret %= MOD;
      x++;
    }
    return ret;
  }
  public static long Comb2(long n, long r)
  {
    long Nume = 1;
    long Deno = 1;

    if (r > n - r) r = n - r;
    for (long i = 1; i <= r; ++i)
    {
      Deno *= i;
      Nume *= n - i + 1;
    }
    return Nume / Deno;
  }
}
public static class Utils
{

  public static void Swap<T>(ref T A, ref T B)
  {
    T x = A;
    A = B;
    B = x;
  }
  public static int DigitSum(int N)
  {
    string s = N.ToString();
    int ret = 0;
    for (int i = 0; i < s.Length; ++i) ret += s[i] - '0';
    return ret;
  }
}
class Program
{
  static void Main(string[] args)
  {
    var CompetitiveProgramming = new CompetitiveProgramming();
    CompetitiveProgramming.Solve();
  }
}
public static class io
{
  public static string Str => Console.ReadLine();
  public static string[] Strs => Str.Split(' ');
  public static long[] Longs => Strs.Select(long.Parse).ToArray();
  public static int[] Ints => Strs.Select(int.Parse).ToArray();
  public static char[] Chars => Str.ToArray();
  public static double[] Doubles => Strs.Select(double.Parse).ToArray();
  public static long Long1 => Longs[0];
  public static int Int1 => Ints[0];
  public static char Char1 => Chars[0];
  public static double Double1 => Doubles[0];
  public static long[] VerticalRead(int N) { long[] A = new long[N]; for (int i = 0; i < N; ++i) A[i] = Long1; return A; }
  public static void Write(string a) => Console.WriteLine(a);
  public static void Write(params object[] i) => Write(string.Join(" ", i));
  //public static void Write<T>(IEnumerable<T> a) => Write(string.Join(" ", a));
  public static void Verticalwrite<T>(IEnumerable<T> a) { foreach (var z in a) Write(z); }
  public static void YN(bool i) { if (i) Write("Yes"); else Write("No"); }
}


Compiler output:
a.cc:1:7: error: expected nested-name-specifier before 'System'
    1 | using System;
      |       ^~~~~~
a.cc:2:7: error: expected nested-name-specifier before 'System'
    2 | using System.Collections;
      |       ^~~~~~
a.cc:3:7: error: expected nested-name-specifier before 'System'
    3 | using System.Collections.Generic;
      |       ^~~~~~
a.cc:4:7: error: expected nested-name-specifier before 'System'
    4 | using System.Linq;
      |       ^~~~~~
a.cc:5:7: error: expected nested-name-specifier before 'System'
    5 | using System.Diagnostics;
      |       ^~~~~~
a.cc:6:7: error: expected nested-name-specifier before 'System'
    6 | using System.Text;
      |       ^~~~~~
a.cc:7:7: error: expected nested-name-specifier before 'System'
    7 | using System.Text.RegularExpressions;
      |       ^~~~~~
a.cc:8:7: error: expected nested-name-specifier before 'System'
    8 | using System.Threading.Tasks;
      |       ^~~~~~
a.cc:9:7: error: expected nested-name-specifier before 'System'
    9 | using System.Numerics;
      |       ^~~~~~
a.cc:10:7: error: expected nested-name-specifier before 'System'
   10 | using System.IO;
      |       ^~~~~~
a.cc:11:7: error: expected nested-name-specifier before 'System'
   11 | using System.Runtime.InteropServices;
      |       ^~~~~~
a.cc:12:7: error: expected nested-name-specifier before 'static'
   12 | using static System.Math;
      |       ^~~~~~
a.cc:13:7: error: expected nested-name-specifier before 'static'
   13 | using static Math2;
      |       ^~~~~~
a.cc:14:7: error: expected nested-name-specifier before 'static'
   14 | using static io;
      |       ^~~~~~
a.cc:15:7: error: expected nested-name-specifier before 'static'
   15 | using static Utils;
      |       ^~~~~~
a.cc:19:1: error: expected unqualified-id before 'public'
   19 | public class CompetitiveProgramming
      | ^~~~~~
a.cc:42:1: error: expected unqualified-id before 'public'
   42 | public class Factorical
      | ^~~~~~
a.cc:64:1: error: expected unqualified-id before 'public'
   64 | public static class Math2
      | ^~~~~~
a.cc:130:1: error: expected unqualified-id before 'public'
  130 | public static class Utils
      | ^~~~~~
a.cc:149:20: error: 'string' has not been declared
  149 |   static void Main(string[] args)
      |                    ^~~~~~
a.cc:149:29: error: expected ',' or '...' before 'args'
  149 |   static void Main(string[] args)
      |                             ^~~~
a.cc:154:2: error: expected ';' after class definition
  154 | }
      |  ^
      |  ;
a.cc: In static member function 'static void Program::Main(int*)':
a.cc:151:5: error: 'var' was not declared in this scope
  151 |     var CompetitiveProgramming = new CompetitiveProgramming();
      |     ^~~
a.cc:152:5: error: 'CompetitiveProgramming' was not declared in this scope
  152 |     CompetitiveProgramming.Solve();
      |     ^~~~~~~~~~~~~~~~~~~~~~
a.cc: At global scope:
a.cc:155:1: error: expected unqualified-id before 'public'
  155 | public static class io
      | ^~~~~~