code: func Decode(s string) uint64 {
  	res := uint64(0)
  	l := len(s) - 1
  	for idx := range s {
  		c := s[l-idx]
  		res += uint64(index[c]) * uint64(math.Pow(36, float64(idx)))
  	}
  	return res
  }
docs: // Decode decodes a base36-encoded string.