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 <vector>
#include <set>
#include <algorithm>
#include <cstring>
#include <cstdlib>
#include <string>
#include <map>
using namespace std;

int ChangeTimesFormat(string str){
    int h = atoi(str.substr(0,2).c_str());
    int m = atoi(str.substr(3,2).c_str());
    int s = atoi(str.substr(6,2).c_str());
    int time = h*60*60+m*60+s;
    return time;
}

int main(){
    int n;
    while(cin>>n&&n!=0){
        set<int> events;
        // ðkeyÆµÄA»ÌÉ­Ë·éñÔÌ,·éñÔÌð²×é
        map<int,pair<int,int> > m;
        for(int i = 0; i < n; i++){
            string from;
            string to;
            cin>>from>>to;
            int ft=ChangeTimesFormat(from);
            int tt=ChangeTimesFormat(to);
            events.insert(ft);
            events.insert(tt);
            m[ft].first++;
            m[tt].second++;
        }

        // ñÔÌÅå
        int maxLine=0;
        // »ÝcÁÄ¢éÌñÔÌ
        int cnt=0;
        // Ì¢Ô©çµÄ¢­
        for(map<int,pair<int,int> >::iterator it = m.begin(); it!=m.end(); it++){
            // ©¦ÁÄ«½ñÔðo^
            cnt+=it->second.second;
            // o­·éñÔÌÌûª½¢ÈçÎ
            if(cnt<it->second.first){
                maxLine+=it->second.first-cnt;
                cnt=0;
            }
            else{
                cnt-=it->second.first;
            }
        }
        cout<<maxLine<<endl;
    }
    return 0;
}

C++: #include <bits/stdc++.h>
#define ADAY 86400
using namespace std;

int main(void){
  int n;
  while(cin >> n, n){
    vector < pair < int, int > > t;
    for(int i=0; i < n; i++){
      pair<int, int> tmp;
      int h, m, s;
      scanf("%d:%d:%d", &h, &m, &s);
      tmp.first = h * 3600 + m * 60 + s;
      scanf("%d:%d:%d", &h, &m, &s);
      tmp.second = h * 3600 + m * 60 + s;
      t.push_back(tmp);
    }

    int ans = 0, movin = 0, ind = 0;
    queue<int> q;
    for(int now=0; now <= ADAY; now++){
      while(!q.empty() && now == q.front()){
        movin--;
        q.pop();
      }
      if(now == t[ind].first){
        q.push(t[ind].second);
        movin++;
        ind++;
        ans = max(ans, movin);
      }
    }
    cout << ans << endl;
  }
  return 0;
}

C++: #include <iostream>
#include <algorithm>
#include <string>
#define N 10000
using namespace std;
int Change(string);
int Change_sup(string);
struct data{
  int s,g;
  bool operator<(const data & right)const{
    if(s!=right.s) return s<right.s;
    return g<right.g;
  }
};
int main(){
  int n,flag[N],com,cnt,i,j;
  string ins,ing;
  struct data d[N];
  while(1){
    cin >> n;
    if(n==0) break;
    for(i=0;i<n;i++){
      cin >> ins >> ing;
      d[i].s=Change(ins);
      d[i].g=Change(ing);
      flag[i]=0;
    }
    sort(d,d+n);
    cnt=0;
    for(i=0;i<n;i++){
      if(flag[i]==0){
    flag[i]=1;
    cnt++;
    com=d[i].g;
    for(j=i+1;j<n;j++){
      if(com<=d[j].s&&flag[j]==0){
        flag[j]=1;
        com=d[j].g;
      }
    }
      }
    }
    cout << cnt << endl;
  }
  return 0;
}
int Change(string str){
  int r;
  string a,b,c;
  a=str.substr(0,2);
  b=str.substr(3,2);
  c=str.substr(6,2);
  r=Change_sup(a+b+c);
  return r;
}
int Change_sup(string str){
  int len=str.size(),x=1,ret=0,i=0;
  while(len){
    ret=ret*x+(str[i]-'0');
    x=10;
    i++;
    len--;
  }
  return ret;
}

C++: #include<bits/stdc++.h>
using namespace std;

//define
#define ALL(a) a.begin(),a.end()
#define REP(i,n) for(int i=0;i<n;i++)
#define RREP(i,n) for(int i=n-1;i>=0;i--)
#define debug(x) if(1) cout<<#x<<":"<<x<<endl;
#define DEBUG(x) if(1) cout<<#x<<":"<<x<<endl;
#define ll long long

//constant
const int MOD=1000000007;
const int INF=INT_MAX/3-1;
const double EPS=1e-9;
const int dx[]={1,0,-1,0};
const int dy[]={0,1,0,-1};

//typedef
typedef vector<int> vi;
typedef vector<vector<int>> vvi;






int main(){
    int n;
    while(cin>>n,n){
        vector<pair<int,bool>> timer;
        string buf;
        REP(i,n){
            REP(j,2){
            cin>>buf;
            int hh=stoi(buf.substr(0,2));
            int mm=stoi(buf.substr(3,2));
            int ss=stoi(buf.substr(6,2));
            timer.push_back(make_pair(ss+mm*60+hh*60*60,j));
            }

        }
        sort(ALL(timer),[](pair<int,bool> lef,pair<int,bool> rig)
        {return lef.first<rig.first ||
                lef.first==rig.first && !lef.first;});
        int running=0;
        int stop=0;
        REP(i,n*2){
            if(!timer[i].second){
                if(stop)
                    stop--;
                else
                    running++;


            }
 else if(timer[i].second){
                stop++;


            }



        }
            cout<<running<<endl;




    }




    return 0;
}

C++: #include <cstdio>
#include <iostream>
#include <algorithm>
#include <map>
#include <vector>
using namespace std;
vector<pair<int,int> > v[2];
int main(void){
  int res;
  int n,f;
  while(cin >> n && n){
    f = res = 0;
    v[0].clear();
    for(int i = 0; i < n; i++){
      int a,b,c,d;
      scanf("%d:%d:%d",&a,&b,&c);
      d = a*3600 + b*60 + c;
      scanf("%d:%d:%d",&a,&b,&c);
      c = a*3600 + b*60 + c;
      v[0].push_back(make_pair(d,c));
    }

    while((int)v[f].size()){
      res++;
      int b = v[f][0].second;
      v[(f+1)%2].clear();
      for(int i = 1; i < (int)v[f].size(); i++){
	if(v[f][i].first < b){
	  v[(f+1)%2].push_back(v[f][i]);
	}
      }
      f = (f+1)%2;
    }
    cout << res << endl;
  }
}