CF245F Log Stream Analysis

You've got a list of program warning logs. Each record of a log stream is a string in this format: "2012-MM-DD HH:MM:SS:MESSAGE" (without the quotes). String "MESSAGE" consists of spaces, uppercase and lowercase English letters and characters "!", ".", ",", "?". String "2012-MM-DD" determines a correct date in the year of 2012. String "HH:MM:SS" determines a correct time in the 24 hour format. The described record of a log stream means that at a certain time the record has got some program warning (string "MESSAGE" contains the warning's description). Your task is to print the first moment of time, when the number of warnings for the last $ n $ seconds was not less than $ m $ .

The first line of the input contains two space-separated integers $ n $ and $ m $ $ (1

If there is no sought moment of time, print -1. Otherwise print a string in the format "2012-MM-DD HH:MM:SS" (without the quotes) — the first moment of time when the number of warnings for the last $ n $ seconds got no less than $ m $ .