var out = 0
var max_out = -1
var max_times = []

ARGF.each { |line|
    out += (line ~~ /OUT/ ? 1 : -1)
    if (out > max_out) {
        max_out = out
        max_times = []
    }
    if (out == max_out) {
        max_times << line.split(' ')[3]
    }
}

say "Maximum simultaneous license use is #{max_out} at the following times:"
max_times.each {|t| say "  #{t}" }