Pastebin

using System;
using System.Windows.Forms;
using System.Runtime.InteropServices;

namespace Request_Excel
{
    public partial class Form1 : Form
    {
        static readonly IntPtr HWND_TOPMOST = new IntPtr(-1);
        static readonly IntPtr HWND_NOTOPMOST = new IntPtr(-2);
        static readonly IntPtr HWND_TOP = new IntPtr(0);
        static readonly IntPtr HWND_BOTTOM = new IntPtr(1);
        const UInt32 SWP_NOSIZE = 0x0001;
        const UInt32 SWP_NOMOVE = 0x0002;
        const UInt32 TOPMOST_FLAGS = SWP_NOMOVE | SWP_NOSIZE;

        [DllImport("user32.dll")]
        [return: MarshalAs(UnmanagedType.Bool)]
        public static extern bool SetWindowPos(IntPtr hWnd, IntPtr hWndInsertAfter, int X, int Y, int cx, int cy, uint uFlags);


        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            SetWindowPos(this.Handle, HWND_TOPMOST, 0, 0, 0, 0, TOPMOST_FLAGS);
        }

        private void button1_Click(object sender, EventArgs e)
        {
            bool result = Int32.TryParse(tb_number1.Text, out int a_);
            if (result && a_ <= 25 && a_ >= 0)
            {
                bool result2 = Int32.TryParse(tb_number2.Text, out int b_);
                if (result2 && b_ <= 25 && b_ >= 0)
                {
                    int c = (a_ + b_) % 25;
                    if (c == 0)
                        tb_answer.Text = "25";
                    else
                        tb_answer.Text = Convert.ToString(c);
                }
                else
                    MessageBox.Show("Please enter a valid number between 0-25");
            }
            else
                MessageBox.Show("Please enter a valid number between 0-25");
        }
    }
}