gets
hour = 0
min = 0;
while l = gets
    h1,m1,h2,m2 = l.split(/ |:/).map(&:to_i)
    if h1 > h2
        hour += (24 - h1) + h2
    else
        hour += h2 - h1
    end

    if m1 > m2
        min += (60 - m1) + m2
        hour -= 1
    else
        min += m2 - m1
    end
end

if min >= 60
    hour += min / 60
    min %= 60
end

puts hour * 60 + min