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>
using namespace std;

#define MAX 24*60*60

int main(){

  int train[MAX];
  int N;

  while(1){
    cin >> N;
     if(N == 0) break;
     int ans = 0;
     for(int i = 0 ; i < MAX ; i++){
       train[i] = 0;
     }    


    int h1,m1,s1,h2,m2,s2;
    char tmp;
    for(int i = 0; i < N ; i++){
    
      cin  >> h1 >> tmp >> m1 >> tmp >> s1 >> h2 >> tmp >> m2 >> tmp >> s2;
      // cout << h1 << " " << m1 << " " << s1 << " " << h2 << tmp << m2 << tmp << s2 <<endl;
      if(train[s1 + 60*m1 + 60*60*h1] == 0){
	ans++;
	for(int i = 0 ; i < s1 + 60*m1 + 60*60*h1 ;i++){
	  train[i]++;
	} 
	for(int i = s2 + 60*m2 + 60*60*h2 ; i < MAX ;i++){
	  train[i]++;
	} 
      } 
      else{
	for(int i =  s1 + 60*m1 + 60*60*h1 ; i <= s2 + 60*m2 + 60*60*h2 ;i++){
	  if(train[i] > 0) train[i]--;
	} 
      }
    }
    cout << ans << endl;
  }  
  return 0;
}

C++: // clang-format off
#include <bits/stdc++.h>
#define int long long
#define main signed main()
// #define main int main()
#define loop(i, a, n) for (int i = (a); i < (n); i++)
#define rep(i, n) loop(i, 0, n)
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()
#define prec(n) fixed << setprecision(n)
#define stlice(from, to) substr(from, (to) - (from) + 1)
#define pb push_back
#define mp make_pair
#define mt make_tuple
#define fi first
#define se second
using namespace std;
using pii = pair<int, int>;
using vi = vector<int>;
using vd = vector<double>;
using vc = vector<char>;
using vb = vector<bool>;
using vs = vector<string>;
using vpii = vector<pii>;
using vvi = vector<vi>;
using vvb = vector<vb>;
using vvpii = vector<vpii>;
template<typename A> using fn = function<A>;
constexpr int INF = sizeof(int) == sizeof(long long) ? 1000000000000000000LL : 1000000000;
constexpr int MOD = 1000000007;
constexpr double PI = acos(-1);
template<typename A, typename B> bool cmin(A &a, const B &b) { return a > b ? (a = b, true) : false; }
template<typename A, typename B> bool cmax(A &a, const B &b) { return a < b ? (a = b, true) : false; }
constexpr bool odd(const int &n) { return n & 1; }
constexpr bool even(const int &n) { return !odd(n); }
void solve();
main { solve(); return 0; }
// clang-format on

void solve() {
  int n;
  while (cin >> n, n) {
    vpii v(n);
    rep(i, n) {
      int h, m, d;
      char gomi;
      cin >> h >> gomi >> m >> gomi >> d;
      int l = h * 3600 + m * 60 + d;
      cin >> h >> gomi >> m >> gomi >> d;
      int r   = h * 3600 + m * 60 + d;
      v[i].fi = l;
      v[i].se = r;
    }
    sort(all(v));
    priority_queue<int, vector<int>, greater<int>> q;
    q.push(v[0].se);
    loop(i, 1, n) {
      if (q.top() <= v[i].fi) q.pop();
      q.push(v[i].se);
    }
    cout << q.size() << endl;
  }
}

C++: #include <bits/stdc++.h>
#include<algorithm>
#define int long long
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define INF 1000000000000
int MOD=1000000007;

signed main() {
int tt;
cin>>tt;
while(tt){
  vector<int> byou(86401);
  rep(i,tt){
    string t1,t2;
    cin>>t1>>t2;
    int iri,de;
    iri=(((int)t1[0]-48)*10+((int)t1[1]-48))*3600+(((int)t1[3]-48)*10+(int)t1[4]-48)*60+((int)t1[6]-48)*10+(int)t1[7]-48;
    de=(((int)t2[0]-48)*10+((int)t2[1]-48))*3600+(((int)t2[3]-48)*10+(int)t2[4]-48)*60+((int)t2[6]-48)*10+(int)t2[7]-48;
    byou[iri]++;
    byou[de]--;
  }
  vector<int>s(86402);
int tmax=0;
  rep(i,86401){
    s[i+1]=s[i]+byou[i];
    tmax=max(tmax,s[i+1]);
  }

  cout<<tmax<<endl;
  cin>>tt;
}
}

C++: #include <iostream>
#include <cstdio>
#include <string>
#include <queue>
#include <functional>
using namespace std;
#define rep(i,n) for(int i=0;i<(n);++i)
#define rep1(i,n) for(int i=1;i<=(n);++i)
#define all(c) (c).begin(),(c).end()
typedef pair<int,int> P;
priority_queue<P,vector<P>,greater<P> > que;
int main(){
	while(true){
		int n;
		cin >> n;
		if(n==0) break;
		rep(i,n){
			string x,y;
			cin >> x >> y;
			int a=stoi(x.substr(0,2))*3600+stoi(x.substr(3,2))*60+stoi(x.substr(6,2));
			int b=stoi(y.substr(0,2))*3600+stoi(y.substr(3,2))*60+stoi(y.substr(6,2));
			que.push(P(b,0));
			que.push(P(a,1));
		}
		int now=0,ans=0;
		while(!que.empty()){
			P q=que.top();
			que.pop();
			if(q.second==0) now++;
			else{
				if(now>0) now--;
				else ans++;
			}
		}
		cout << ans << endl;
	}
}

C++: #include <iostream>
#include <algorithm>
#include <string>
#define TIME 86400
using namespace std;

int flag[TIME + 1];

int main() {
  while (true) {
    int n;
    cin >> n;
    if (n == 0) return 0;
    string p[n], q[n];
    int a[n][8], b[n][8], s[n], t[n];
    for (int i = 0; i < n; i++)
      cin >> p[i] >> q[i];
    for (int i = 0; i < n; i++) {
      for (int j = 0; j < 8; j++) {
	if (j == 2 || j == 5) continue;
	a[i][j] = p[i][j] - '0';
	b[i][j] = q[i][j] - '0';
      }
    }
    
    for (int i = 0; i < n; i++) {
      s[i] = a[i][0] * 36000 + a[i][1] * 3600 + a[i][3] * 600 + a[i][4] * 60
	+ a[i][6] * 10 + a[i][7];
      t[i] = b[i][0] * 36000 + b[i][1] * 3600 + b[i][3] * 600 + b[i][4] * 60
	+ b[i][6] * 10 + b[i][7];
    }
    
    for (int i = 0; i < TIME + 1; i++)
      flag[i] = 0;
    
    for (int i = 0; i < n; i++)
      for (int j = s[i]; j < t[i]; j++)
	flag[j]++;
    
    int max = 0;
    for (int i = 1; i < TIME + 1; i++)
      if (flag[i] > max) max = flag[i];

    cout << max << endl;
  }
}