#include <cstdio>
#include <map>
using namespace std;

int enc(int a, int b, int c)
{
  return a*3600+b*60+c;
}

int main()
{
  int n; 
  while(scanf("%d",&n),n) {
    multimap<int,int> mm;

    for (int i=0;i<n;++i) {
      int a1,b1,c1,a2,b2,c2;
      scanf("%d:%d:%d",&a1,&b1,&c1);
      scanf("%d:%d:%d",&a2,&b2,&c2);
      mm.insert(make_pair(enc(a1,b1,c1),enc(a2,b2,c2)));
    }

    int ans=0;
    while(!mm.empty()) {
      ++ans;
      int cur=mm.begin()->second;
      mm.erase(mm.begin());
      while(1) {
	multimap<int,int>::iterator it=mm.lower_bound(cur);
	if (it==mm.end()) break;
	cur=it->second;
	mm.erase(it);
      }
    }
    printf("%d\n",ans);
  }
}