longest := ""
	for k := 0; k < len(str)/2+1; k++ {
		candidate := string(str[k])
		for i := 1; true; i++ {
			// avoid overrun or underrun
			if (k-i < 0) || (k+i > len(str)-1) {
				break
			}
			// two identical bytes

	if str == "" {
		return ""
	}
	var longest string
	for k := 1; k < len(str)/2+1; k++ {
		var candidate string
		for i := 1; k-i > -1 && k+i < len(str); i++ {

				candidate = string(str[k-i]) + candidate + string(str[k+i])

				candidate = str[k-i : k+i+1]

	if len(longest) > 1 {
		return longest
	}
	return ""

	return longest

	if str == "" {
		return ""
	}