# Here your code !
A_DAY = 24 * 60
n = gets.to_i
puts n.times.map { 
    s, e = gets.split.map {|hm| 
        h,m = hm.split(":").map(&:to_i)
        60 * h + m
    }
    
    (e - s) % A_DAY
}.inject(:+)