[DllImport("user32.dll")]
    internal static extern IntPtr SetForegroundWindow(IntPtr hWnd);

    [DllImport("user32.dll")]
    internal static extern bool ShowWindow(IntPtr hWnd, int nCmdShow); //ShowWindow needs an IntPtr

    private static void FocusProcess()
    {
        IntPtr hWnd; //change this to IntPtr
        Process[] processRunning = Process.GetProcesses();
        foreach (Process pr in processRunning)
        {
            if (pr.ProcessName == "notepad")
            {
                hWnd = pr.MainWindowHandle; //use it as IntPtr not int
                ShowWindow(hWnd, 3);
                SetForegroundWindow(hWnd); //set to topmost
            }
        }
    }