/////////////////////////////No.70 睡眠の重要性！
    //入力文字読み取り
    var inputall = require('fs').readFileSync('/dev/stdin', 'utf8');

    //すべて受け取り改行で区切って格納
      var input = inputall.split("\n");

    //睡眠数を数値に変換
      var sleepall = Number(input[0]);

    var sum =0
    //時間、分を数値に変換
      for (var i = 1; i <= sleepall; i++) {
          var hour2 = input[i].split(" ");
          var hour =[]
          var minute = []
          var minute1 = 0
          var minute2 = 0

          for (var j = 0; j < hour2.length; j++) {
               hour[j] = hour2[j].split(":").map(Number)
          }
          //時間、分を 分に変換
          var minute1 = hour[0][0] * 60 + hour[0][1];
          var minute2 = hour[1][0] * 60 + hour[1][1];

          if (minute1 > minute2) {
              sum += (1440 - minute1) + minute2;
          } else {
              sum += minute2 - minute1;
          }

      }
   
      console.log(sum);