Go: package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
	"strings"
)

func main() {
	io := NewIo()
	defer io.Flush()
	for {
		n := io.NextInt()
		if n == 0 {
			break
		}
		accum := make([]int, 86401)
		for i := 0; i < n; i++ {
			s, e := io.Next(), io.Next()
			hs, _ := strconv.Atoi(s[:2])
			ms, _ := strconv.Atoi(s[3:5])
			ss, _ := strconv.Atoi(s[6:8])
			accum[hs*60*60+ms*60+ss]++
			he, _ := strconv.Atoi(e[:2])
			me, _ := strconv.Atoi(e[3:5])
			se, _ := strconv.Atoi(e[6:8])
			accum[he*60*60+me*60+se]--
		}
		ans := 0
		for i := 1; i < 86401; i++ {
			accum[i] += accum[i-1]
			ans = intMax(accum[i], ans)
		}
		io.Println(ans)
	}
}

func intMax(a, b int) int {
	if a < b {
		return b
	}
	return a
}

// I/O template
type Io struct {
	reader    *bufio.Reader
	writer    *bufio.Writer
	tokens    []string
	nextToken int
}

func NewIo() *Io {
	return &Io{
		reader: bufio.NewReader(os.Stdin),
		writer: bufio.NewWriter(os.Stdout),
	}
}

func (io *Io) Flush() {
	err := io.writer.Flush()
	if err != nil {
		panic(err)
	}
}

func (io *Io) NextLine() string {
	var buff []byte
	for {
		line, isPrefix, err := io.reader.ReadLine()
		if err != nil {
			panic(err)
		}
		buff = append(buff, line...)
		if !isPrefix {
			break
		}
	}
	return string(buff)
}

func (io *Io) Next() string {
	for io.nextToken >= len(io.tokens) {
		line := io.NextLine()
		io.tokens = strings.Fields(line)
		io.nextToken = 0
	}
	s := io.tokens[io.nextToken]
	io.nextToken++
	return s
}

func (io *Io) NextInt() int {
	i, err := strconv.Atoi(io.Next())
	if err != nil {
		panic(err)
	}
	return i
}

func (io *Io) NextFloat() float64 {
	i, err := strconv.ParseFloat(io.Next(), 64)
	if err != nil {
		panic(err)
	}
	return i
}

func (io *Io) Println(a ...interface{}) {
	fmt.Fprintln(io.writer, a...)
}

func (io *Io) Printf(format string, a ...interface{}) {
	fmt.Fprintf(io.writer, format, a...)
}

func (io *Io) PrintIntSlice(a []int) {
	b := []interface{}{}
	for _, x := range a {
		b = append(b, x)
	}
	io.Println(b...)
}

func (io *Io) PrintStringSlice(a []string) {
	b := []interface{}{}
	for _, x := range a {
		b = append(b, x)
	}
	io.Println(b...)
}

func Log(name string, value interface{}) {
	fmt.Fprintf(os.Stderr, "%s=%+v\n", name, value)
}

func ExampleIo() {
	io := NewIo()
	defer io.Flush()
	a := make([]int, 0, 3)
	a[0], a[1], a[2] = io.NextInt(), io.NextInt(), io.NextInt()
	io.Println(a)
	io.PrintIntSlice(a)
	Log("io", a)
}

C++: #include <iostream>
#include <string>
#include <algorithm>
using namespace std;
static const int N = 10000;
int Change(string);
int main(){
  int n,cnt,check[N],ok,flag,Max,sh[N],sm[N],ss[N],eh[N],em[N],es[N],i,j;
  int comh,comm,coms;
  string start[N],end[N],sub;
  while(1){
    cin >> n;
    cnt=0;
    if(n==0) break;
    for(i=0;i<n;i++){
      cin >> start[i] >> end[i];
      check[i]=-1;
      sub=start[i].substr(0,2);
      sh[i]=Change(sub);
      sub=start[i].substr(3,2);
      sm[i]=Change(sub);
      sub=start[i].substr(6,2);
      ss[i]=Change(sub);
      sub=end[i].substr(0,2);
      eh[i]=Change(sub);
      sub=end[i].substr(3,2);
      em[i]=Change(sub);
      sub=end[i].substr(6,2);
      es[i]=Change(sub);
    }
    for(i=0;i<n;i++){
      if(check[i]==-1){
	check[i]=i;
	comh=eh[i];
	comm=em[i];
	coms=es[i];
	for(j=i+1;j<n;j++){
	  if(check[j]==-1){
	    ok=0;
	    if(comh==sh[j]){
	      if(comm==sm[j]){
		if(coms<=ss[j]) ok=1;
	      }
	      else if(comm<sm[j]) ok=1;
	    }
	    else if(comh<sh[j]) ok=1;
	    if(ok==1){
	      comh=eh[j];
	      comm=em[j];
	      coms=es[j];
	      check[j]=i;
	    }
	  }
	}
      }
    }
    Max=0;
    for(i=0;i<n;i++){
      Max=max(Max,check[i]);
    }
    cout << Max+1 << endl;
  }
  return 0;
}
int Change(string sub){
  int ret=0,x=1,i;
  for(i=0;i<2;i++){
    ret=ret*x+(sub[i]-'0');
    x=10;
  }
  return ret;
}

C++: #include <iostream>
#include <vector>
#include <algorithm>
#include <utility>

using namespace std;

inline int parse(const string& s)
{
    const int hour = stoi(s.substr(0, 2));
    const int minute = stoi(s.substr(3, 2));
    const int second = stoi(s.substr(6, 2));
    return hour * 3600 + minute * 60 + second;
}

int main()
{
    while (true) {
        int n;
        cin >> n;
        if (n == 0) {
            break;
        }
        using P = pair<int, int>;
        vector<P> train(n);
        vector<int> number(n, -1);
        for (int i = 0; i < n; i++) {
            string s, e;
            cin >> s >> e;
            train[i] = make_pair(parse(s), parse(e));
        }
        sort(train.begin(), train.end());
        int numbered = 0;
        int num = 0;
        while (numbered < n) {
            int start = 0;
            for (int i = 0; i < n; i++) {
                if (train[i].first >= start and number[i] == -1) {
                    number[i] = num;
                    numbered++;
                    start = train[i].second;
                }
            }
            num++;
        }
        cout << num << endl;
    }
    return 0;
}

C++: //include
//------------------------------------------
#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>
#include <climits>
#include <queue>
 
using namespace std;
 
int main(){
  int N;
  while(cin >> N, N){
    //vector<PII> tms;
    int range[24*60*60+1];
    fill(range, range+24*60*60+1, 0);
    REP(i,N){
      int h[2], m[2], s[2];
      scanf("%2d:%2d:%2d", &h[0], &m[0], &s[0]);
      scanf("%2d:%2d:%2d", &h[1], &m[1], &s[1]);
      int st = h[0]*60*60+m[0]*60+s[0], et = h[1]*60*60+m[1]*60+s[1];
      ++range[st], --range[et];
    }
    //SORT(tms);
    int ans = 0, acc = 0;
    REP(i,24*60*60){
      acc += range[i];
      ans = max(ans, acc);
    }
    cout << ans << endl;
  }  
   
  return 0;
}

C++: #include "bits/stdc++.h"

using namespace std;

using ll = long long;

template<typename T> using V = std::vector<T>;
using Vi = V<int>;
using VVi = V<V<int>>;
using Vl = V<ll>;
using VVl = V<V<ll>>;
using Vs = V<string>;

template<typename T1, typename T2> using P = std::pair<T1, T2>;
using Pii = P<int, int>;
using Pll = P<ll, ll>;
using Pdd = P<double, double>;

template<typename T1, typename T2> using M = std::map<T1, T2>;
using Mii = M<int, int>;
using Msi = M<string, int>;

#define REP(i,n) for(int i=0;i<(int)(n);++i)
#define REP2(i,s,e) for(int i=(int)(s);i<(int)(e);++i)
#define RREP(i,s,e) for(int i=(int)(s);i>=(int)(e);--i)
#define FOR(i,c) for(__typeof((c).begin())i=(c).begin(),ie=(c).end();i!=ie;++i)
#define ALL(c) (c).begin(), (c).end()

const double PI = acos(-1);
const ll MOD = 1e9+7;

int n;
string s;

int main() {
    while (true) {
        cin >> n;
        if (n == 0) break;

        V<Pii> v(n);
        REP(i, n) {
            int h, m, s;
            int h2, m2, s2;
            scanf("%02d:%02d:%02d %02d:%02d:%02d\n", &h, &m, &s, &h2, &m2, &s2);
            v[i] = {s + m*100 + h*10000, s2 + m2*100 + h2*10000};
        }

        Vi cnt(3e6, 0);
        FOR(i, v) {
            cnt[i->first] += 1;
            cnt[i->second] -= 1;
        }

        int sum = 0, maxi = -1;
        REP(i, 3e6) {
            sum += cnt[i];
            maxi = max(maxi, sum);
        }
        std::cout << maxi << '\n';
    }

    return 0;
}