using System;
using System.Linq;

public class Test
{
  private static int? SwapMax(int n)
  {
    var a = n.ToString().ToCharArray();
    var c = a.Max();
    var i = Array.IndexOf(a, c);
    if (i == 0) return null;
    a[i] = a[i-1];
    a[i-1] = c;
    return int.Parse(new String(a));
  }
	
  public static void Main()
  {
    foreach (var n in new int[] {23, 32, 4056, 4056456, 8, 99, 89, 98, 103})
      Console.WriteLine("{0} => {1}", n, SwapMax(n));
  }
}