function main() {
  // get events from jan 1 and jan 2
  return Events({
    from_date: "2015-02-01",
    to_date: "2016-01-08",
    event_selectors: [{event: "LAUNCH_SESSION_START"}]
  }).groupByUser(['properties.idfa'], function (state, events) {
        state = state || { first: events[0].time }
        state.last = events[events.length - 1].time;
        var interval = state.last-state.first;
        if(interval>5259492000){        return state;};
}).filter( function(result) {
        if(result.value !== null) {
                return result.key
};});


};