#include <bits/stdc++.h>
using namespace std;

/////////////////// メイン ///////////////////

int main () {
  
  //////////////////// 入力 ////////////////////

  int n;
  cin >> n;

  vector<string> a(n), b(n);
  for (int i=0; i<n; i++) {
    cin >> a.at(i) >> b.at(i);
    if (a.at(i).at(1)==':') a.at(i).insert(a.at(i).begin(),'0');
    if (a.at(i).size()==4) a.at(i).insert(a.at(i).begin()+3,'0');
    if (b.at(i).at(1)==':') b.at(i).insert(b.at(i).begin(),'0');
    if (b.at(i).size()==4) b.at(i).insert(b.at(i).begin()+3,'0');
  }

  //////////////// 出力変数定義 ////////////////

  int result = 0;

  //////////////////// 処理 ////////////////////

  for (int i=0; i<n; i++) {
    int x = 0;
    x += (a.at(i).at(0)-'0')*600;
    x += (a.at(i).at(1)-'0')*60;
    x += (a.at(i).at(3)-'0')*10;
    x += (a.at(i).at(4)-'0')*1;
    int y = 0;
    y += (b.at(i).at(0)-'0')*600;
    y += (b.at(i).at(1)-'0')*60;
    y += (b.at(i).at(3)-'0')*10;
    y += (b.at(i).at(4)-'0')*1;
    if (y<x) y += 1440;
    result += y-x;
  }

  //////////////////// 出力 ////////////////////

  cout << result << endl;

  //////////////////// 終了 ////////////////////

  return 0;

}