using System;

using System.IO;

using System.Security.Cryptography;

​

namespace Rextester{

    public class Program{

        public static void Main(string[] args){

            var weight = 20.80;

            var weight1 = 0.30;

            var weight2 = 7.50;

            var weight3 = 13.00;

            var nWeight1 = Math.Round((decimal)weight1, 2);

            var nWeight2 = Math.Round((decimal)weight2, 2);

            var nWeight3 = Math.Round((decimal)weight3, 2);

​

            var w1 = 1.00;

            var w2 = 3.00;

            var w3 = 16.00;

            Console.WriteLine("original " + weight);

            weight += weight1 - w1;

            Console.WriteLine("after 1 change (added" + weight - w1 + " + weight);

            if(weight < w1) {

                weight = w1;

                Console.WriteLine("w1");

            }

            weight += weight2 - w2;

            Console.WriteLine("after 2 change " + weight);

            if(weight < w2) {

                weight = w2;

                Console.WriteLine("w2");

            }           

            weight += weight2 - w3;

            Console.WriteLine("after 3 change " + weight);

            if(weight < w3) {

                weight = w3;

                Console.WriteLine("w3");

            }

            Console.WriteLine("final " + weight);

            //Console.WriteLine(weight1 + weight2 + weight3);

            //Console.WriteLine(nWeight1);

        }

    }

}