function rot13(str) { // LBH QVQ VG!

var decoded = ""; // a string variable which concatenates the decoded strings
  for (var i = 0; i < str.length; i++){
if(str.charCodeAt(i) >= 65 && str.charCodeAt(i) <=77) {//convert letters A-M into its ascii code
decoded += String.fromCharCode(str.charCodeAt(i) + 13);// add those letters to decode add 13 to make it N-Z
  } else if(str.charCodeAt(i) >= 78 && str.charCodeAt(i) <=90) {
decoded += String.fromCharCode(str.charCodeAt(i) - 13);//similarly in the second if we are repeating this N-Z converting them to A-M
  }

  else {
    decoded += str[i]; //we are taking care of the characters which are not A-Z
    }
}
  return decoded;
}