let N = int <| stdin.ReadLine()
let t (s:string) =
    let a = s.Split(':')
    let b = (int a.[0] * 60) + int a.[1]
    b
let f (s:string) =
    let a = s.Split(' ')
    let b,c = t a.[0], t a.[1]
    if b <= c then c - b
    else 1440 - (b - c)
seq { for _ in 1..N -> stdin.ReadLine() }
|> Seq.map f
|> Seq.sum
|> printfn "%d"