using System;
using System.Text;

public class Test
{
	public static void Main()
	{
	Console.Write("Enter string: ");
var text = Console.ReadLine();
StringBuilder sb = new StringBuilder("", text.Length);
int count = 0;
foreach (var el in text)    {
     if (Char.IsWhiteSpace(el)) 
         count++;  
     else {
        if (count==1)
           sb.Append('%',1);
        if (count>1)
           sb.Append(' ',1);
        sb.Append(el,1);
        count = 0;
     }
 }
Console.WriteLine($"New string: {sb.ToString()}");
	}
}