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

int main(){
    vector< vector<int> > trains;
    vector<int> buf(86401,0);
    int n,h,m,s,bf,bt,i,j,add_f;
    while(1){
        scanf("%d",&n);
        if(!n){break;}
        for(i=0;i<n;i++){
            scanf("%d:%d:%d",&h,&m,&s);
            bf=h*3600+m*60+s;
            scanf("%d:%d:%d",&h,&m,&s);
            bt=h*3600+m*60+s;
            auto bs=buf.begin();
            if(trains.empty()){
                fill(bs+bf,bs+bt,1);
                trains.push_back(buf);
                fill(bs+bf,bs+bt,0);
            }
            else{
                add_f=1;
                for(auto it=trains.begin();it!=trains.end();it++){
                    auto p=(*it).begin();
                    int fn=count(p+bf,p+bt,1);
                    if(fn==0 || (*(p+bf)==1 && *(p+bt)==1 && fn==2)){
                        fill(p+bf,p+bt,1);
                        add_f=0;
                        break;
                    }
                }
                if(add_f){
                    fill(bs+bf,bs+bt,1);
                    trains.push_back(buf);
                    fill(bs+bf,bs+bt,0);
                }
            }
        }
        printf("%lu\n",trains.size());
        trains.clear();
        trains.shrink_to_fit();
    }
    return 0;
}

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,w;
  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;
	w=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){
	      check[j]=w;
	      comh=eh[j];
	      comm=em[j];
	      coms=es[j];
	    }else w=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 <sstream>
#include <fstream>
#include <string>
#include <vector>
#include <deque>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <algorithm>
#include <functional>
#include <utility>
#include <bitset>
#include <cmath>
#include <cstdlib>
#include <ctime>
#include <cstdio>

#define rep(i, n) for(int (i) = 0; (i) < (n); (i)++)

class Solve {
public:
	Solve() {};
	~Solve() {};

	void solver() {
		std::vector<int> results;
		while (1) {
			int n;
			std::cin >> n;
			if (!n) break;

			std::string str;
			rep(i, n) {
				times.push_back(std::make_pair(0, 0));
				std::cin >> str;
				times.back().first = std::stoi(str.substr(6, 2)) + std::stoi(str.substr(3, 2)) * 60 + std::stoi(str.substr(0, 2)) * 3600;
				std::cin >> str;
				times.back().second = std::stoi(str.substr(6, 2)) + std::stoi(str.substr(3, 2)) * 60 + std::stoi(str.substr(0, 2)) * 3600;
			}
			//
			std::reverse(times.begin(), times.end());
			//???????????????????????????
			std::vector<int> usingTrain; //int?????°?????????
			int maxTrain = 0;
			while (!times.empty()) {
				int leave = times.back().first;
				int arrive = times.back().second; times.pop_back();
				//??°???????????????????????????
				std::sort(usingTrain.begin(), usingTrain.end(), std::greater<int>());
				//????????°???
				if (!usingTrain.empty()) {
					//????????°?????????????????????????????°???
					if (leave <= usingTrain.back()) {
						usingTrain.pop_back();
					}
				}
				//??????
				usingTrain.push_back(arrive);
				if (maxTrain < usingTrain.size()) maxTrain = usingTrain.size();
			}
			results.push_back(maxTrain);
		}
		for (auto& x : results) {
			std::cout << x << std::endl;
		}
	}
private:
	std::vector<std::pair<int, int>> times;
};

int main() {
	Solve solve;
	solve.solver();
	return 0;
}