Android : syncing between phone and web algorithm

i have a simple note application in two platform, One in mobile(Android & iOS) and other one is web based. I want that this two sync.

My problem is that: How i can determine that which version of a note(android or web) is newer and that text has to be sync? In fact, I need a sync algorithm. If i use timestamp, if users date time in his phone goes to wrong date time, syncing system throws to problem. I want newest edit syncs to all clients.

In the end, What is the best method for this? I want to have best sync method