function autoTab(input, len, e) {
    var keyCode = e.keyCode;
    var filter = [0, 8, 9, 16, 17, 18, 37, 38, 39, 40, 46];
    if (input.value.length >= len && !containsElement(filter, keyCode)) {
        input.value = input.value.slice(0, len);
        input.form[(getIndex(input) + 1) % input.form.length].focus();
    }
function containsElement(arr, ele) {
    var found = false, index = 0;
    while(!found && index < arr.length)
    if(arr[index] == ele)
    found = true;
    else
    index++;
    return found;
  }

  function getIndex(input) {
    var index = -1, i = 0, found = false;
    while (i < input.form.length && index == -1)
    if (input.form[i] == input)index = i;
    else i++;
    return index;
  }
  return true;
}