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 <fstream>
#include <stdio.h>
#include <queue>
#include <vector>
#include <string>

using namespace std;

int n;
priority_queue<pair<int, int>, vector<pair<int, int> >, greater<pair<int, int> > > q;

int cir_time(string str){
    int h = stoi(str.substr(0, 2));
    int m = stoi(str.substr(3, 2));
    int s = stoi(str.substr(6, 2));
    s+= h*60*60+m*60;
    return s;
}

int main(int argc, const char * argv[]) {
    // input from txt
    
    /////////
    //write//
    /////////
    
    while(1){
        cin >> n;
        if(n==0)break;
        for(int i=0; i<n; i++){
            string str1, str2;
            cin >> str1 >> str2;
            q.push(make_pair(cir_time(str1), 0));
            q.push(make_pair(cir_time(str2), 1));
        }
        int cnt=0;
        int ans=0;
        while(!q.empty()){
            pair<int, int> f = q.top();
            q.pop();
            int t = f.first;
            int type = f.second;
            if(type == 0){
                cnt++;
                if(!q.empty() && q.top().first == t){
                    continue;
                }
                ans = max(ans, cnt);
            }
            else{
                cnt--;
                if(!q.empty() && q.top().first != t){
                    ans=max(ans, cnt);
                }
            }
        }
        
        cout << ans << endl;
    }
    
    return 0;
}

C++: #include<bits/stdc++.h>
#define _ ios_base::sync_with_stdio(0);cin.tie(0);
#define REP(i,n) for(int i=0;i<(int)(n);i++)

using namespace std;

const int MAX_N=1000;

pair<int,int> p[MAX_N+1];

int main(){ _;
  int n,a=0,b=0,c=0,d=0,e=0,f=0;
  while(cin>>n,n!=0){
    REP(i,n){
      scanf("%02d:%02d:%02d %02d:%02d:%02d",&a,&b,&c,&d,&e,&f);
      p[i]=make_pair(a*3600+b*60+c,d*3600+e*60+f);
    }
    priority_queue<int,vector<int>,greater<int> > que;
    int maxTrain=0;
    sort(p,p+n);
    REP(i,n){
      while(!que.empty()&&que.top()<=p[i].first)
	que.pop();
      que.push(p[i].second);
      maxTrain=max(maxTrain,(int)que.size());
    }
    cout<<maxTrain<<endl;
  }
}

C++: #include<iostream>
#include<set>
#include<string>
using namespace std;

int main(){
	while(true){
		int m,pool=0,total=0;
		multiset<string> run;
		cin>>m;
		if(m==0)break;
		for(int i=0;i<m;i++){
			string dep,arv;
			cin>>dep>>arv;
			run.insert(arv);
			for(multiset<string>::iterator ita=run.begin();(*ita)<=dep;){
				pool++;
				run.erase(ita++);
			}
			if(pool==0){
				total++;
			}else{
				pool--;
			}
		}
		cout<<total<<endl;
	}
	return 0;
}

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

#define fi first
#define se second
#define repl(i,a,b) for(int i=(int)(a);i<(int)(b);i++)
#define repr(i,n) for(int i=(int)(n-1);i>=0;i--)
#define rep(i,n) repl(i,0,n)
#define each(itr,v) for(auto itr:v)
#define pb(s) push_back(s)
#define all(x) (x).begin(),(x).end()
#define dbg(x) cout << #x" = " << x << endl
#define print(x) cout << x << endl
#define maxch(x,y) x=max(x,y)
#define minch(x,y) x=min(x,y)
#define uni(x) x.erase(unique(all(x)),x.end())
#define exist(x,y) (find(all(x),y)!=x.end())
#define bcnt(x) bitset<32>(x).count()

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> P;
typedef pair<P, int> PPI;
typedef pair<int, P> PIP;
typedef pair<ll, ll> PL;
typedef pair<P, ll> PPL;
typedef set<int> S;

#define INF INT_MAX/3
#define MAX_N 1000000001


int main(){
  cin.sync_with_stdio(false);
  int n;
  while(cin >> n, n) {
    string s;
    int time[24 * 3600] = {};
    rep(i, n) {
      cin >> s;
      time[stoi(s.substr(0, 2)) * 3600 + stoi(s.substr(3, 2)) * 60 + stoi(s.substr(6, 2))]++;
      cin >> s;
      time[stoi(s.substr(0, 2)) * 3600 + stoi(s.substr(3, 2)) * 60 + stoi(s.substr(6, 2))]--;
    }
    int maxi = 0, tmp = 0;
    rep(i, 24 * 3600) {
      tmp += time[i];
      maxch(maxi, tmp);
    }
    cout << maxi << endl;
  }

  return 0;
}