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 <sstream>
#include <vector>
#include <algorithm>
#define INF 1 << 28
using namespace std;

typedef pair<int,int> P;

int main ()
{
    int n;
    while (cin >> n, n) {
        string str1, str2;
        vector<P> time;
        while (n--) {
            cin >> str1 >> str2;
            for (int i = 0; i < str1.size(); i++) {
                if (str1[i] == ' ') {
                    str1[i] = str2[i] = ' ';
                }
            }

            stringstream ss1, ss2;
            ss1 << str1;
            ss2 << str2;

            int t1, t2, t3;
            ss1 >> t1 >> t2 >> t3;
            int s = t1 * 60 * 60 + t2 * 60 + t3;
            ss2 >> t1 >> t2 >> t3;
            int e = t1 * 60 * 60 + t2 * 60 + t3;

            time.push_back(P(s,e));
        }

        time.push_back(P(INF,INF));
        vector<int> st, et;
        for (int i = 0; i < time.size(); i++) {
            st.push_back(time[i].first);
            et.push_back(time[i].second);
        }

        int k = 0, l = 0;
        int tmp = 0, MAX = 0;
        while (st[k] != INF || et[l] != INF) {
            if (st[k] < et[l]) {
                tmp++;
                k++;
            } else if (k > 0 && (st[k - 1] + 60 * 60) <= et[l]) {
                tmp--;
                l++;
            } else {
                MAX = MAX < tmp + 1 ? tmp + 1 : MAX;
            }
            MAX = MAX < tmp ? tmp : MAX;
        }

        cout << MAX << endl;
    }

    return 0;
}

C++: #include<bits/stdc++.h>

using namespace std;

int main(){
 
  while(1){
	vector<int> time(24*60*60,0);
    int n;
	cin >> n;

	if(n == 0)
	  break;
	
	for(int i = 0;i<n;i++){
	  int h,m,s;
	  
	  scanf("%d:%d:%d",&h,&m,&s);
	  time[h * (60*60) + m * 60 + s]++;
	  
	  scanf("%d:%d:%d",&h,&m,&s);
	  time[h * (60*60) + m * 60 + s]--;	  
	}

	int train = 0;
	int train_max = 0;
	
	for(int i = 0;i < 24*60*60;++i){
	  train += time[i];
	  train_max = max(train,train_max);
	  
	}

	cout << train_max << endl;
	
  }
  
  return 0;

}

C++: #include<bits/stdc++.h>
#define pb push_back
using namespace std;
typedef long long ll;
typedef pair<int,int> P;
const ll INF=1000000000LL;
const ll MOD=1000000007LL;
const ll MAX=100010;
int main(){
	int n;
	while(cin>>n,n){
		vector<P> v;
		for(int i=0;i<n;i++){
			for(int j=0;j<2;j++){
				int h,m,s;
				scanf("%d:%d:%d",&h,&m,&s);
				int t=h*3600+m*60+s;
				if(j){
					v.pb(P(t,-1));
				}else{
					v.pb(P(t,1));
				}
			}
		}
		sort(v.begin(),v.end());
		int ans=0;
		int r=0;
		for(int i=0;i<2*n;i++){
			r+=v[i].second;
			ans=max(r,ans);
		}
		cout<<ans<<endl;
	}
	return 0;
}

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

#define REP(i,n) for(int i=0;i<(n);i++)
#define REAP(i,a,n) for(int i=(a);i<(n);i++)
#define YES cout<<"Yes"<<endl
#define NO cout<<"No"<<endl
#define fr first
#define sc second
#define pb push_back
#define All(v) v.begin(),v.end()
typedef long long ll;

int main(){
    ios::sync_with_stdio(false);
    int n;
    while(cin >> n,n){
        string st,en;
        int table[100000]={};
        REP(i,n){
            cin >> st>>en;
            int stim=0;
            stim+=(st[0]-'0')*10+(st[1]-'0');
            stim*=60;
            stim+=(st[3]-'0')*10+(st[4]-'0');
            stim*=60;
            stim+=(st[6]-'0')*10+(st[7]-'0');
            int etim=0;
            etim+=(en[0]-'0')*10+(en[1]-'0');
            etim*=60;
            etim+=(en[3]-'0')*10+(en[4]-'0');
            etim*=60;
            etim+=(en[6]-'0')*10+(en[7]-'0');

            table[stim]+=1;
            table[etim]+=-1;
        }
        int res=0,sum=0;
        for(int i=0;i<100000;i++){
//            if(table[i])cout << i/3600 <<" "<<table[i]<<endl;
            sum+=table[i];
            res=max(res,sum);
        }
        cout << res << endl;
    }
}

C++: #include<iostream>
#include<cstdio>
#include<vector>
#include<string>
#include<algorithm>

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

using namespace std;

int main()
{

  int n ;
  int Sh,Sm,Ss;
  int Eh,Em,Es;
  int max = -1;
  long int Sindex,Eindex;
  vector<int> time(240001);


  while(cin >> n && n!=0)
    {

      fill(time.begin(),time.end(),0);

      rep(i,n){

        scanf("%d:%d:%d",&Sh,&Sm,&Ss);
        scanf("%d:%d:%d",&Eh,&Em,&Es);

        Sindex = Sh*10000 + Sm*100 + Ss;
        Eindex = Eh*10000 + Em*100 + Es;

        time[Sindex]++;
        time[Eindex]--;

      }

      rep(i,time.size())
        if(i > 0)
          time[i] += time[i-1];

      rep(i,time.size())
        if(max < time[i])
          max = time[i];

      cout << max << endl;

    }

  return 0;

}

C++: #include <cstdio>
#include <algorithm>

using namespace std;

int second(int h, int m, int s) {
	return h * 3600 + m * 60 + s;
}

int main() {
	int n;
	int train[24 * 60 * 60];
	const int trainNum = sizeof train / sizeof train[0];
	while (true) {
		scanf("%d", &n);
		if (n == 0) {
			break;
		}
		for (int i = 0; i < trainNum; i++) {
			train[i] = 0;
		}
		for (int i = 0; i < n; i++) {
			int h1, m1, s1, h2, m2, s2;
			scanf("%d:%d:%d %d:%d:%d", &h1, &m1, &s1, &h2, &m2, &s2);
			int tmp1 = second(h1, m1, s1);
			int tmp2 = second(h2, m2, s2);
			train[tmp1]++;
			train[tmp2]--;
		}
		int a = 0;
		int ans = 0;
		for (int i = 0; i < trainNum; i++) {
			a += train[i];
			ans = max(a, ans);
		}
		printf("%d\n", ans);

	}

	return 0;
}