using System;

public class Test
{
	public static void Main()
	{
		decimal val = 123.456789M;
		Console.WriteLine(RoundDown(val, 0.001M));
		Console.WriteLine(RoundDown(val, 10));
	}
	
	public static decimal RoundDown(decimal val, decimal pos) {
		return pos * Math.Truncate(val / pos);
	}
}