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>
using namespace std;
#define REP(i, a, n) for(int i=a; i<n; i++)
#define INF 1000000000

int main()
{
	int N;
	cin >> N;
	int min_mem = 0, max_mem = INF;
	REP(i, 0, N) {
		int aa, bb;
		cin >> aa >> bb;
		min_mem = max(min_mem, aa);
		max_mem = min(max_mem, bb);
	}

	if (min_mem <= N && min_mem <= max_mem) {
		cout << min_mem - 1 << endl;
	}
	else {
		cout << 0 << endl;
	}

	return 0;
}

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

using namespace std;

template <class T>
struct SegmentTree/*{{{*/
{
    vector<T> nodes, stocks;
    int size;
    SegmentTree(int size) : size(size) {
        nodes.resize(size*4, 0);
        stocks.resize(size*4, 0);
    }

    void maintain_consistency(int pos) {
        /*
        // ノードの値が子の合計と一致しない場合，不完全な更新が行なわれているため
        // 下のノードに伝搬させる．
        int children_sum = nodes[pos*2+1] + nodes[pos*2+2];
        if(children_sum != nodes[pos]) { 
            //cout << "maintain: " << pos << ' ' << nodes[pos] << ' ' << children_sum << endl;
            int diff = nodes[pos] - children_sum;
            nodes[pos*2+1] += diff/2;
            nodes[pos*2+2] += diff/2;
        }
        */
        if(stocks[pos] > 0) {
            stocks[pos*2+1] += stocks[pos] / 2;
            stocks[pos*2+2] += stocks[pos] / 2;
            nodes[pos] += stocks[pos];
            stocks[pos] = 0;
        }
    }

    // [left, right) に対するクエリ．
    // 現在のノードはpos で， [pl, pr) を表わしている．
    T get_inner(int left, int right, int pos, int pl, int pr) {
        //cout << left << ' ' << right << ' ' << pos << ' ' <<  pl << ' ' << pr << endl;
        if(pr <= left || right <= pl) return 0; // 交差しない
        if(left <= pl && pr <= right) return nodes[pos] + stocks[pos]; // 完全に含まれる

        maintain_consistency(pos);

        const int center = (pl+pr) / 2;
        T lv = get_inner(left, right, pos*2+1, pl, center);
        T rv = get_inner(left, right, pos*2+2, center, pr);
        return lv + rv;
    }

    T get(int left, int right) {
        return get_inner(left, right, 0, 0, size);
    }

    T add_inner(int left, int right, int pos, int pl, int pr) {
        //cout << left << ' ' << right << ' ' << pos << ' ' <<  pl << ' ' << pr << endl;
        if(pr <= left || right <= pl) return stocks[pos] + nodes[pos]; // 交差しない
        if(left <= pl && pr <= right) {
            //cout << "tail: " << pl << ' ' << pr << endl;
            stocks[pos] += pr-pl;
            return stocks[pos] + nodes[pos]; // 完全に含まれる
        }

        maintain_consistency(pos);

        const int center = (pl+pr)/2;
        T lv = add_inner(left, right, pos*2+1, pl, center);
        T rv = add_inner(left, right, pos*2+2, center, pr);
        return nodes[pos] = lv+rv;
    }

    T add(int left, int right) {
        return add_inner(left, right, 0, 0, size);
    }
};/*}}}*/

int main() {
    cin.tie(0);
    ios::sync_with_stdio(0);
    int N;
    cin >> N;
    SegmentTree<int> segtree(N+1);
    for(int i = 0; i < N; ++i) {
        int minval, maxval;
        cin >> minval >> maxval;
        segtree.add(minval-1, maxval);
    }
    //cout << "Added" << endl;
    //cout << segtree.nodes[0] << ' ' << segtree.nodes[1] << ' ' << segtree.nodes[2] << endl;
    int ans = 0;
    for(int n = N; n >= 0; --n) {
        //cout << segtree.nodes[0] << ' ' << segtree.nodes[1] << ' ' << segtree.nodes[2] << endl;
        const int val = segtree.get(n, n+1);
        //cout << val << endl;
        if(val >= n) {
            ans = n;
            break;
        }
    }
    cout << ans << endl;
    return 0;
}

C++: #include <bits/stdc++.h>
#define ll long long
ll mod=1000000007;
#define vl vector<ll>
#define pl pair<ll,ll>
#define rep(i,b) for(ll i=0;i<b;i++)
#define all(v) (v).begin(),(v).end()
using namespace std;

bool compare_by_b(pair<ll, ll> a, pair<ll, ll> b) {
    if(a.second != b.second){
        return a.second < b.second;
    }else{
        return a.first < b.first;
    }
}

ll lcm(int a, int b){
    return (ll)a * b / __gcd(a, b);
}
ll t[100005];
int main(){
    ll n,a,b; cin>>n;
    for(int i=0;i<n;i++){
        cin>>a>>b;
        t[a-1]++;
        t[b]--;
    }
    ll ans=0;
    for(int i=1;i<=100000;i++){
        t[i]+=t[i-1];
        if(i<=t[i])ans=i;
    }
    cout<<ans<<endl;
}

C++: #include<iostream>
#include<cstdio>
using namespace std;
int main()
{
  int friends[100005]={};
  int i;
  int n;
  int a,b;
  int max=0;

  cin>>n;
  for(i=0;i<n;i++){
    cin>>a>>b;
    friends[a]++;
    friends[b+1]--;
    //    cout<<"i"<<i<<endl;
  }
  for(i=1;i<100005;i++)
    friends[i]+=friends[i-1];
  for(i=0;i<100005;i++)
    if(friends[i]>=i-1)
      max=i-1;

  cout<<max<<endl;
}

C++: #include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <climits>
#include <cfloat>
#include <ctime>
#include <map>
#include <utility>
#include <set>
#include <iostream>
#include <memory>
#include <string>
#include <vector>
#include <algorithm>
#include <functional>
#include <sstream>
#include <complex>
#include <stack>
#include <queue>
#include <numeric>
#include <list>

using namespace std;

#ifdef _MSC_VER
#define __typeof__ decltype
template <class T> int __builtin_popcount(T n) { return n ? 1 + __builtin_popcount(n & (n - 1)) : 0; }
#endif

#define foreach(it, c) for (__typeof__((c).begin()) it=(c).begin(); it != (c).end(); ++it)
#define all(c) (c).begin(), (c).end()
#define rall(c) (c).rbegin(), (c).rend()
#define popcount __builtin_popcount
           
#define rep(i, n) for (int i = 0; i < n; ++i)

template <class T> void max_swap(T& a, const T& b) { a = max(a, b); }
template <class T> void min_swap(T& a, const T& b) { a = min(a, b); }

const double EPS = 1e-10;
typedef long long ll;
typedef pair<int, int> pint;


int main()
{
    int n;
    static int new_ok[100010];
    scanf("%d", &n);
    rep (i, n)
    {
	int a, b;
	scanf("%d%d", &a, &b);
	++new_ok[min(b, n + 1)];
	--new_ok[min(a - 1, n + 1)];
    }
    ++new_ok[n + 1];

    int res = -3, ok = 0;
    for (int i = n + 1; i > 0; --i)
    {
	if (ok)
	    ok += new_ok[i];
	if (ok >= i)
	{
	    res = i - 1;
	    break;
	}
    }
    printf("%d\n", res);
}

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

//define
#define ALL(a) a.begin(),a.end()
#define REP(i,n) for(int i=0;i<n;i++)
#define RREP(i,n) for(int i=n-1;i>=0;i--)
#define debug(x) if(1)cout<<#x<<":"<<x<<endl;
#define DEBUG(x) if(1)cout<<#x<<":"<<x<<endl;
#define ll long long

//typedef
typedef vector<int> vi;
typedef vector<vector<int>> vvi;

bool possible(int num, vector<int> &a, vector<int> &b) {
	int cnt = 0;
	for (int i = 0; i < a.size(); i++) {
		if (a[i] <= num && num <= b[i]) {
			cnt++;
		}
	}
	if (cnt >= num)
		return true;
	else
		return false;

}

int main(){
	int n;
		vector<int> a(n), b(n);
		for (int i = 0; i < n; i++) {
			cin >> a[i] >> b[i];
		}
		int lb = 0;
		int ub = n+1 ;
		while (ub - lb > 1) {
			int mid = (ub + lb) / 2;
			if (possible(mid,a,b)) {
				lb = mid;
			}
			else {
				ub = mid;
			}
		}
		cout << lb << endl;


	return 0;
}