#include <bits/stdc++.h>
#define rep(i, ss, ee) for (int i = ss; i < ee; ++i)
using namespace std;

std::vector<int> split_int(std::string src, char delimiter) {
  int first = 0;
  int last = src.find_first_of(delimiter);
  std::vector<int> result;
  while (first < src.size()) {
    std::string subStr(src, first, last - first);
    result.emplace_back(std::stoi(subStr));
    first = last + 1;
    last = src.find_first_of(delimiter, first);
    if (last == std::string::npos) {
      last = src.size();
    }
  }
  return result;
}

int main() {
  int N;
  int ans = 0;
  string s;
  cin >> N;
  vector<int> vs, ve;
  int ts, te;
  const int h24 = 24 * 60;
  rep(i, 0, N) {
    cin >> s;
    vs = split_int(s, ':');
    cin >> s;
    ve = split_int(s, ':');

    ts = vs[0] * 60 + vs[1];
    te = ve[0] * 60 + ve[1];

    if (ts > te) {
      te += h24;
    }

    ans += te - ts;
  }
  cout << ans << endl;
  getchar();
}