#include <iostream>
#include <string>
#include <vector>
#include <sstream>
#include <fstream>

using namespace std;

vector<string> split(const string& input, char delimiter) {
    istringstream stream(input);

    string field;
    vector<string> result;
    while (getline(stream, field, delimiter)) {
      result.push_back(field);
    }
    return result;
}

int main() {


  int n,sum;
  sum = 0;
  cin >> n;
  for (int i = 0; i < n; i++) {
    string x,y;
    cin >> x >> y;
    //xをsplitしてそれぞれ出力
    //cout << split(x, ':')[1] << "\n";

    int hx = stoi(split(x,':')[0]);
    int mx = stoi(split(x,':')[1]);
    int hy = stoi(split(y,':')[0]);
    int my = stoi(split(y,':')[1]);
    //cout << hx << "\n";
    int st = hx * 60 + mx;
    int en = hy * 60 + my;
    //cout << hx << " " << st << "\n";
    if(en - st < 0){
      sum += 1440 + en - st;
    }else{
      sum += en - st;
    }
    //cout << sum << "\n";
  }
  cout << sum << "\n";

  return 0;
}