Go: // A Way to Invite Friends(友だちの誘い方)
// http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=2331&lang=ja
package main

import (
	"bufio"
	"fmt"
	"math"
	"os"
	"strconv"
)

const N_MAX = 1000001

func main() {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)

	n := nextInt(sc)
	allow_list := make([]int, N_MAX+100)
	nMax := 0

	for i := 0; i < n; i++ {
		a, b := nextInt(sc), nextInt(sc)
		allow_list[a] += 1
		allow_list[b+1] += -1
		nMax = int(math.Max(float64(nMax), float64(b)))
	}

	for i := 2; i <= N_MAX; i++ {
		allow_list[i] += allow_list[i-1]
	}

	res := 0
	for i := 2; i <= nMax; i++ {
		if i-1 <= allow_list[i] { // i人誘う時に行きたい人の人数を超えないか(自分を含めて)
			res = i - 1 // 自分は除く
		}
	}

	fmt.Println(res)
}

func nextInt(sc *bufio.Scanner) int {
	sc.Scan()
	i, err := strconv.Atoi(sc.Text())
	if err != nil {
		panic(err)
	}
	return i
}

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

using namespace std;

int n;

int main()
{
    cin >> n;
    vector< vector<int> > ab(n + 2, vector<int>(0) );
    vector<int> away(n + 2, 0);
    int a,b;
    for(int i = 0; i < n; i++){
        cin >> a >> b;
        if(a < n + 2) ab[a].push_back(b);
    }
    sort(ab.begin(), ab.end());
    int count = 1;
    int m = 1;
    for(int j = 1; j < n + 2; j++){
        if(ab[j].size() == 0) continue;
        if(count + ab[j].size() < j){
            count = count + ab[j].size();
            for (int k = 1; k <= ab[j].size(); k++)
            {
                away[(int)ab[j][k - 1] + 1]++;
            }
            continue;
        }
        for(int k = 1; k <= ab[j].size(); k++){
            count++;
            count -= away[count];
            //cout << count << endl;
            m = max(m, count);
            away[(int)ab[j][k - 1] + 1]++;
        }
    }
    //for(int k = 0; k < n + 2; k++) cout << away[k] << endl;
    cout << m - 1 << endl;
    return 0;
}

C++: #include <stdio.h>

int n, x, y, imos[100003], table[100002];

int main()
{
    scanf("%d", &n);
    
    for(int i = 0; i < n; i++)
    {
        scanf("%d", &x);
        scanf("%d", &y); y++;
        
        imos[x]++;
        imos[y]--;
    }
    
    for(int i = 1; i <= 100001; i++)
    {
        table[i] = table[i - 1] + imos[i];
    }
    
    int ret = 0;
    
    for(int i = 1; i <= 100001; i++)
    {
        if(i - 1 <= table[i])
        {
            ret = i;
        }
    }
    
    printf("%d\n", ret);
    
    return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;
using ll = long long;
using VI = vector<ll>;
using VV = vector<VI>;
using VS = vector<string>;
using PII = pair<ll, ll>;

// tourist set
template <typename A, typename B>
string to_string(pair<A, B> p);

template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p);

template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p);

string to_string(const string& s) {
  return '"' + s + '"';
}

string to_string(const char* s) {
  return to_string((string) s);
}

string to_string(bool b) {
  return (b ? "true" : "false");
}

string to_string(vector<bool> v) {
  bool first = true;
  string res = "{";
  for (int i = 0; i < static_cast<int>(v.size()); i++) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(v[i]);
  }
  res += "}";
  return res;
}

template <size_t N>
string to_string(bitset<N> v) {
  string res = "";
  for (size_t i = 0; i < N; i++) {
    res += static_cast<char>('0' + v[i]);
  }
  return res;
}

template <typename A>
string to_string(A v) {
  bool first = true;
  string res = "{";
  for (const auto &x : v) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(x);
  }
  res += "}";
  return res;
}

template <typename A, typename B>
string to_string(pair<A, B> p) {
  return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}

template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " + to_string(get<2>(p)) + ")";
}

template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " + to_string(get<2>(p)) + ", " + to_string(get<3>(p)) + ")";
}

void debug_out() { cerr << '\n'; }

template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
  cerr << " " << to_string(H);
  debug_out(T...);
}

#ifdef LOCAL
#define debug(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
#define debug(...) 42
#endif
// tourist set end

template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }

#define FOR(i,a,b) for(ll i=(a);i<(b);++i)
#define rep(i,b) FOR(i, 0, b)
#define ALL(v) (v).begin(), (v).end()
#define p(s) cout<<(s)<<'\n'
#define p2(s, t) cout << (s) << " " << (t) << '\n'
#define br() p("")
#define pn(s) cout << (#s) << " " << (s) << '\n'
#define p_yes() p("YES")
#define p_no() p("NO")
#define SZ(x) ((int)(x).size())
#define SORT(A) sort(ALL(A))
#define RSORT(A) sort(ALL(A), greater<ll>())
#define MP make_pair

void no(){p_no(); exit(0);}
void yes(){p_yes(); exit(0);}

const ll mod = 1e9 + 7;
const ll inf = 1e18;
const double PI = acos(-1);

// ei1333's BIT
struct BIT {
  VI data;
  BIT(){}
  BIT(ll sz) {
    resize(sz);
  }
  void resize(ll sz){
    data.assign(++sz, 0);
  }
  ll sum(ll k) {
    ll ret = 0;
    for(++k; k > 0; k -= k & -k) ret += data[k];
    return (ret);
  }
  void add(ll k, ll x) {
    for(++k; k < (ll)data.size(); k += k & -k) data[k] += x;
  }
};
 
// 区間更新・区間和
struct Range{
  BIT P, Q;
  Range(ll sz){
    P.resize(sz+1);
    Q.resize(sz+1);
  }
  // [a, b)
  void update(ll a, ll b, ll w){
    P.add(a, -w*a);
    P.add(b,  w*b);
    Q.add(a,  w);
    Q.add(b, -w);
  }
  // [0, c)
  ll simple_sum(ll c){
    return P.sum(c) + Q.sum(c) * c;
  }
  // [a, b)
  ll sum(ll a, ll b){
    return simple_sum(b) - simple_sum(a);
  }
};

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);

    // input
    ll N; 
    cin >> N;

    Range range(100100);

    rep(i, N){
      ll a, b; cin >> a >> b;
      range.update(a, b+1, 1);
    }
    ll ma = 0;
    FOR(i, 1, 100100){
      // i人がいいな
      ll n = range.sum(i, i+1);
      if(n+1>=i){
        chmax(ma, i-1);
      }
    }
    p(ma);
    return 0;
}

C++: #include <stdio.h>
#include <iostream>
#include <vector>
#include <algorithm>
#include <string>

using namespace std;


int main(){
	int n;
	int a[100000], b[100000];

	cin >> n;
	int max = 0, min = 100001;
	for (int i = 0; i < n; ++i){
		cin >> a[i] >> b[i];
		if (a[i] < min) min = a[i];
		else if (b[i] > max) max = b[i];
	}

	int max_friends = 0;
	for (int i = min; i < max; ++i){
		int friends = 0;
		for (int j = 0; j < n; ++j){
			if (a[j] <= i-1 && b[j] >= i-1){
				++friends;
			}
		}
		if (friends == i-1 && --friends > max_friends){
			max_friends = friends;
		}
	}

	cout << max_friends << endl;



	return 0;
}