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

struct E {
    int t;
    char type;
    E(int t, char type) : t(t), type(type) {}
    bool operator<(const E& o) const {
        return t < o.t;
    }
};

int main() {
    int n;
    while (scanf("%d", &n), n != 0) {
        vector<E> es;
        for (int i = 0; i < n; i++) {
            int h, m, s;
            int _h, _m, _s;
            scanf("%d:%d:%d %d:%d:%d", &h, &m, &s, &_h, &_m, &_s);
            es.push_back(E(h*3600+m*60+s, 'o'));
            es.push_back(E(_h*3600+_m*60+_s, 'i'));
        }
        sort(es.begin(), es.end());
        int cnt = 0;
        int total = 0;
        for (int i = 0; i < es.size(); i++) {
            if (es[i].type == 'o') {
                cnt++;
                total = max(total, cnt);
            } else {
                cnt--;
            }
        }
        cout << total << endl;
    }
    return 0;
}

C++: #include <iostream>
#include <cstdio>
using namespace std;
int main(void){
    int n;
    int hh,mm,ss,st,en;
    int time[86401];
    char ch;
    while(1){
        cin >> n;
        if(n == 0)  break;
        for(int j = 0; j < 86400; j++){
            time[j] = 0;
        }
        for(int i = 0; i < n; i++){
            cin >> hh >> ch >> mm >> ch >> ss;
            st = hh * 3600 + mm * 60 + ss;
            cin >> hh >> ch >> mm >> ch >> ss;
            en = hh * 3600 + mm * 60 + ss;
            for(int j = st; j < en; j++){
                time[j]++;
            }
        }
        
        int maxt = 0;
        for(int i = 0; i < 86400; i++){
            if(maxt < time[i])  maxt = time[i];
        }
        
        cout << maxt << endl;
        
    }
    
    return 0;
}

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

using namespace std;

typedef long long Int;
typedef vector<int> vint;
typedef pair<int,int> pint;
typedef vector<string> vstring;
typedef vector<pint> vpint;

struct Edge{int to,from,cost;};

#ifdef DEBUG
#define debug cout
#else
stringstream __ss__;
#define debug __ss__
#endif

template<class T> void pv(T a, T b) { for (T i = a; i != b; ++i) debug << *i << " "; debug << endl; }
template<class T> void chmin(T &t, T f) { if (t > f) t = f; }
template<class T> void chmax(T &t, T f) { if (t < f) t = f; }
int in() { int x; scanf("%d", &x); return x; }

#define rep(i,n) for(int i=0;i<(n);++i)
#define repd(i,n) for(int i=(n)-1;i>=0;i--)
#define repn(i,m,n) for(int i=(m);i<=(n);++i)
#define repnd(i,m,n) for(int i=(n)-1;i>=(m);i--)
#define rep0(i,n) for(i=0;i<(n);++i)
#define all(n) n.begin(),n.end()
#define sz(n) ((int)(n).size())
#define IL for(;;)
#define MP make_pair
#define PB push_back
#define SS stringstream
#define X second
#define Y first
#define PUTLINE debug<<"LINE:"<<__LINE__<<endl;

const int INF = 2147483647/3;
const double EPS = 1e-10;
const double PI = acos(-1.0);

const int dx[]={1,-1,0,0,1,-1,1,-1,0};
const int dy[]={0,0,1,-1,1,-1,-1,1,0};

vint train;

int main() {
	IL{
		train.clear();
		int n=in();
		if(n==0)break;
		string f,t;
		int from,to;
		rep(i,n){
			cin>>f>>t;
			from=(f[0]-'0')*100000+(f[1]-'0')*10000+(f[3]-'0')*1000+(f[4]-'0')*100+(f[6]-'0')*10+f[7]-'0';
			to=(t[0]-'0')*100000+(t[1]-'0')*10000+(t[3]-'0')*1000+(t[4]-'0')*100+(t[6]-'0')*10+t[7]-'0';
			if(sz(train)>0&&train[0]<=from){
				train[0]=to;
			}else{
				train.PB(to);
			}
			sort(all(train));
		}
		cout<<sz(train)<<endl;
	}
	return 0;
}

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

int main(){
  while(1){
  int n;
  cin >> n;
  if(!n) break;
  vector<int> train(24*60*60,0);
  for(int i=0; i<n; i++){
    int h,m,s;
    scanf("%d:%d:%d",&h,&m,&s);
    int from = h*60*60 + m*60 + s;
    scanf("%d:%d:%d",&h,&m,&s);
    int to = h*60*60 + m*60 + s;
    for(int i=from; i<to; i++){
      train[i] ++;
    }
  }
  cout << *max_element(train.begin(),train.end()) << endl;
  }
}