using System;
using System.Text;
 
public class Test
{
	public static void Main()
	{
		string s = "NEW ITEM:1_BELT:3_JEANS:1_BELT:1_SUIT 3 PCS:1_SHOES:1";
                var array = s.Split(new char[] { ':' }, StringSplitOptions.RemoveEmptyEntries);
                StringBuilder sb = new StringBuilder();
                foreach (var item in array)
                {
                    if (Char.IsDigit(item[0]))
                    {
                        sb.Append(":" + item[0]);
                    }
                }
 
                Console.WriteLine(sb); //:1:3:1:1:1:1
	}
}

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