func dateValue(_ inpt:String) ->Int {
    let tmp = inpt.split(separator: ":").map{Int($0)!}
    return tmp[0]*60+tmp[1]
}

let inputCount = Int(readLine()!)!

var ans:Int = 0

for i in 1...inputCount {
    let inpt = readLine()!.split(separator: " ").map(String.init)
    let stTime = dateValue(inpt[0])
    var edTime = dateValue(inpt[1])
    if(edTime<stTime) {
        edTime+=1440
    }
    ans += (edTime - stTime)
}

print(ans)