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

int main(){
    vector<vector<int>> trains;
    vector<int> buf(86401,0);
    int i,k,h,m,s,ts,te,n,isd;
    
    while(1){
        scanf("%d",&n);
        if(!n){break;}
        for(i=0;i<n;i++){
            scanf("%d:%d:%d",&h,&m,&s);
            ts=h*3600+m*60+s;
            scanf("%d:%d:%d",&h,&m,&s);
            te=h*3600+m*60+s;

            if(trains.empty()){
                fill(buf.begin()+ts,buf.begin()+te,1);
                trains.push_back(buf);
                fill(buf.begin()+ts,buf.begin()+te,0);
            }
            else{
                isd=0;
                for(auto j=trains.begin();j!=trains.end()&&!isd;j++){
                    for(k=ts+1;k<=te-1;k++){
                        if((*j)[k]){
                            isd=1;
                            fill((*j).begin()+ts,(*j).begin()+te,1);
                            break;
                        }
                    }
                }
                if(isd){
                    fill(buf.begin()+ts,buf.begin()+te,1);
                    trains.push_back(buf);
                    fill(buf.begin()+ts,buf.begin()+te,0);
                }
            }
        }
        printf("%lu\n",trains.size());
    }
    return 0;
}

C++: #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 <queue>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <complex>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>
#include <fstream>
#include <stdio.h>

using namespace std;

//conversion
//------------------------------------------
inline int toInt(string s) {int v; istringstream sin(s);sin>>v;return v;}
template<class T> inline string toString(T x) {ostringstream sout;sout<<x;return sout.str();}

//typedef
//------------------------------------------
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<double> VEC;
typedef vector<VEC> MAT;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef pair<int, PII> TIII;
typedef long long LL;
typedef vector<LL> VLL;
typedef vector<VLL> VVLL;
//container util

//------------------------------------------
#define ALL(a)  (a).begin(),(a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define MP make_pair
#define SZ(a) int((a).size())
#define EACH(i,c) for(typeof((c).begin()) i=(c).begin(); i!=(c).end(); ++i)
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort((c).begin(),(c).end())
#define MT(a,b,c) MP(a, MP(b, c))
#define T1 first
#define T2 second.first
#define T3 second.second

//repetition
//------------------------------------------
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n)  FOR(i,0,n)
#define EPS 1.0e-9

int tls[88888];

int main(){
	int n;
	while(cin>>n,n){
		memset(tls, 0, sizeof(tls));
		int x,y,z;
		REP(i,n){
			scanf("%d:%d:%d", &x, &y, &z);
			int t1 = x*1440+60*y+z;
			tls[t1]++;
			scanf("%d:%d:%d", &x, &y, &z);
			int t2 = x*1440+60*y+z;
			tls[t2]--;
		}
		int tmp=0, ret=0;
		REP(i, 86400){
			tmp += tls[i];
			ret=max(ret,tmp);
		}
		cout << ret << endl;
	}
	return 0;
}

C++: #include<map>
#include<set>
#include<list>
#include<cmath>
#include<queue>
#include<stack>
#include<cstdio>
#include<string>
#include<vector>
#include<complex>
#include<cstdlib>
#include<cstring>
#include<numeric>
#include<sstream>
#include<iostream>
#include<algorithm>
#include<functional>

#define mp       make_pair
#define pb       push_back
#define all(x)   (x).begin(),(x).end()
#define rep(i,n) for(int i=0;i<(n);i++)

using namespace std;

typedef    long long          ll;
typedef    unsigned long long ull;
typedef    vector<bool>       vb;
typedef    vector<int>        vi;
typedef    vector<vb>         vvb;
typedef    vector<vi>         vvi;
typedef    pair<int,int>      pii;

const int INF=1<<29;
const double EPS=1e-9;

const int dx[]={1,0,-1,0},dy[]={0,-1,0,1};
int n;
int sch[86410];//秒単位に変換
int main(){
	while(cin>>n,n){
		for(int i = 0;i <=86400;i++){
			sch[i] = 0;
		}
		for(int i = 0;i < n;i++){
			string str;
			int h,m,s;
			cin>>str;
			h = ((str[0]-'0')*10+(str[1]-'0'))*60*60;
			m =((str[3]-'0')*10 +(str[4]-'0'))*60;
			s =(str[6]-'0')*10+(str[7]-'0');
			int dep = h+m+s;
			cin>>str;
			h = ((str[0]-'0')*10+(str[1]-'0'))*60*60;
			m =((str[3]-'0')*10 +(str[4]-'0'))*60;
			s =(str[6]-'0')*10+(str[7]-'0');
			int arr = h+m+s;
			for(int i =dep;i <arr;i++){
				sch[i]+=1;
			}
		}
		int ans = 0;
		for(int i =0;i <=86410;i++){
			ans =max(ans,sch[i]);
		}
		cout <<ans<<endl;
	}
	return 0;
}