public partial class Form1 : Form 

    { 

        [System.Runtime.InteropServices.DllImport("user32.dll")] 

        private static extern short GetAsyncKeyState(Keys vKey); 

        public Form1() 

        { 

            InitializeComponent(); 

        } 

  

        private void Form1_KeyDown(object sender, KeyEventArgs e) 

        { 

            if (e.KeyCode == Keys.ShiftKey) 

            { 

                if (Convert.ToBoolean(GetAsyncKeyState(Keys.LShiftKey))) 

                    MessageBox.Show("Left"); 

                if (Convert.ToBoolean(GetAsyncKeyState(Keys.RShiftKey))) 

                    MessageBox.Show("Right"); 

            } 

        } 

    }