function rot13 (string) {
	var aCode = 'a' . charCodeAt(0);
 	var zCode = 'z' . charCodeAt(0);
	var ACode = 'A' . charCodeAt(0);
	var ZCode = 'Z' . charCodeAt(0);
 	var result = '';
	for (var c = 0; c < string.length; c++) {

		var charCode = string.charCodeAt(c);

		if (charCode >= aCode && charCode <= zCode) {
			charCode = aCode + (charCode - aCode + 13) % 26;
		} else if (charCode >= ACode && charCode <= ZCode) {
			charCode = ACode + (charCode - ACode + 13) % 26;
		}
		
		result += String.fromCharCode(charCode);
	}

	return result;
}