#include <bits/stdc++.h>
#define fastIO (cin.tie(0), cout.tie(0), ios::sync_with_stdio(false))
#define precise(i) fixed << setprecision(i)
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
using namespace std;

int strToMin(string date) {
  int idx = 0;
  for (size_t i = 0; i < date.size(); ++i) {
    if (date[i] == ':')
      idx = (int)i;
  }

  int time = 0;

  // hour
  if (idx == 2) {
    time += stoi(date.substr(0, idx)) * 60;
  } else {
    time += (int)(date[0] - '0') * 60;
  }

  // min
  if (idx + 2 == (int)date.size()) {
    time += (int)(date[idx + 1] - '0');
  } else {
    time += stoi(date.substr(idx + 1));
  }

  return time;
}

int main() {
  fastIO;

  int n;
  cin >> n;

  int sum = 0;
  rep(i, n) {
    string wake, sleep;
    cin >> wake >> sleep;

    int w = strToMin(wake);
    int s = strToMin(sleep);

    if (w > s)
      s += 24 * 60;

    sum += s - w;
  }

  cout << sum << '\n';
}