function fearNotLetter(str) {

  //return str;

  var arr = str.split('');

  var temp = [];

  var start = str.charCodeAt(0);

  var end = str.charAt(str.length - 1).charCodeAt(0);

  for(var i = start; i < end + 1; i++){

    var item = String.fromCharCode(i);

    if(arr[0] !== item){

      temp.push(item);

    }else{

      arr.shift();

    }

  }

  if(temp.length === 0){

    return undefined;

  }else{

    return temp.join('');

  }

}

fearNotLetter("abce");