using System;
using System.Text;

public class Test
{
	public static void Main()
	{
		string bign = "11212131342354364364656121";
		StringBuilder sb = new StringBuilder(bign.Length * 4 / 3);
		int jj = bign.Length % 3;
		
		sb.Append(bign[0]);
		for(int i = 1;i<bign.Length;i++) {
		   if(i % 3 == jj) {
		      sb.Append(",");
		   }
		   sb.Append(bign[i]);	
		}
		
		Console.WriteLine(sb.ToString());
	}
}