@day=60*24

def convert(h,m)
    return h*60+m
end

n=gets.to_i

sum=0
n.times{
    query=gets.chomp.scan(/(\d+):(\d+) (\d+):(\d+)/)[0].map!(&:to_i)
    m1=convert(query[0],query[1])
    m2=convert(query[2],query[3])
    
    if m1>m2
        sum+=@day-m1+m2
    else
        sum+=m2-m1
    end
}

p sum