/**
 *  Osaki (Problem B, Practice Contest for Japan Domestic, 2007-06-24)
 *  by Kenji Inoue, 2007-06-25
 **/

#include <iostream>
#include <string>
#include <vector>

using namespace std;

struct Time {
  string s, e; // start, end
  bool done;
  int operator<(const Time &a) const {
    return s < a.s;
  }
};

int main() {
  int n;
  while (cin >> n, n) {
    vector<Time> ts;
    for (int i=0; i<n; i++) {
      string s, e;
      cin >> s >> e;

      Time t = {s, e, false};
      ts.push_back(t);
    }

    int ans = 0;
    sort(ts.begin(), ts.end());
    for (int i=0; i<ts.size(); i++) {
      if (ts[i].done) { continue; }

      ans++;
      ts[i].done = true;
      string end = ts[i].e;
      for (int j=i+1; j<ts.size(); j++) {
        if (ts[j].done) { continue; }

        if (ts[j].s >= end) {
          ts[j].done = true;
          end = ts[j].e;
        }
      }
    }

    cout << ans << endl;
  }

  return 0;
}