Recently, a ransomware attack called "WannaCry" is infecting computers worldwide, causing great alarm and trepidation.
Operating systems developed by Company W are also vulnerable to such attack. As a reaction, Company W has released a patch for the operating systems on May 21st, 2017. They claim that if and only if the user updates his system after the release date, his system can be well protected.
Now, given the last update date of a system, can you judge whether it is safe or not?
Each date is represented in the format of 8-digits "YYYYMMDD", where "YYYY" is the year (from "0001" to "9999", "MM" is the month (from "01" to "12"), and "DD" is the day (from "01" to "31").
3 20170501 20170521 20170531
unsafe unsafe safe