You can put this solution on YOUR website! "5th" is the ordinal number corresponding to the cardinal number "5".
"45th" is the ordinal number corresponding to the cardinal number "45".
"1st" is the ordinal number corresponding to the cardinal number "1".
"100th" is the ordinal number corresponding to the cardinal number "100".
So
"nth" is the ordinal number corresponding to the cardinal number "n".