Parsing string to TimeSpan

Hey guys, I'm trying to parse some string to TimeSpan . Input string is "01:02:01" and I'm trying it to parse to TimeSpan structure like this

TimeSpan.ParseExact(inputString, "dd:hh:mm", CultureInfo.InvariantCulture)

TimeSpan.ParseExact(inputString, "dd:hh:mm", CultureInfo.InvariantCulture)

(expecting days:hours:minutes) but I got "Input string was not in a correct format." exception. What I'm doing wrong ? Thanks