n = gets.chomp.to_i    
sum = 0
n.times {
    line = gets.chomp.split
    begin_h, begin_m = line[0].split(':').map &:to_i
    end_h, end_m = line[1].split(':').map &:to_i
    if begin_h > end_h
        begin_h -= 24
    elsif begin_h == end_h
        if begin_m > end_m
            begin_m -= 24 * 60
        end
    end
    minute_begin = begin_h * 60 + begin_m
    minute_end = end_h * 60 + end_m
    time = minute_end - minute_begin
    sum += time
}
p sum