document.onkeydown = function(e) {
	var keycode;
	var ctrl;
	var shift;
	var prevent = null;

	// for something else IE
	if (e != null) {
		keycode = e.which;
		ctrl    = typeof e.modifiers == 'undefined' ? e.ctrlKey : e.modifiers & Event.CONTROL_MASK;
		shift   = typeof e.modifiers == 'undefined' ? e.shiftKey : e.modifiers & Event.SHIFT_MASK;
		prevent = function() {
			e.which = 0;
			e.preventDefault();
			e.stopPropagation();
		};
	}
	// for IE
	else {
		keycode = window.event.keyCode;
		ctrl    = window.event.ctrlKey;
		shift   = window.event.shiftKey;
		prevent = function() {
			window.event.keyCode = 0;
			window.event.returnValue = false;
			window.event.cancelBubble = true;
		};
	}

	// prevent
	var keychar = String.fromCharCode(keycode).toUpperCase();
	if (
			(ctrl && keychar == 'C') ||
			(ctrl && keychar == 'X') ||
			(ctrl && keychar == 'P')
	) {
		prevent();
		return false;
	} else {
		return true;
	}
};