Go: package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
//	"strings"
    "sort"
//    "container/heap"
)

/*********** Input **************/
/*
var rdr = bufio.NewReaderSize(os.Stdin, 1000000)

func readLine() string {
	buf := make([]byte, 0, 1000000)
	for {
		l, p, e := rdr.ReadLine()
		if e != nil {
			panic(e)
		}
		buf = append(buf, l...)
		if !p {
			break
		}
	}
	return string(buf)
}*/

func scanInt(sc *bufio.Scanner) int {
    sc.Scan()
    v, _ := strconv.Atoi(sc.Text())
    return v
}
/**************  End Input  **************/

func toInt(str string) int {
	n, _ := strconv.Atoi(str)
	return n
}

type Edge struct {
	to      int
	newTime int
}

type State struct {
	node int
	time int
}


/**************  Cell  *****************/

type Cell struct {
	item *State
	next *Cell
}

func NewCell(x *State, cp *Cell) *Cell {
	newCp := new(Cell)
	newCp.item = x
	newCp.next = cp
	return newCp
}

/************  End Cell  ***************/

/**************  Queue  ****************/

type Queue struct {
	size  int
	front *Cell
	rear  *Cell
}

func NewQue() *Queue {
	return new(Queue)
}

func (q *Queue) Push(x *State) {
	newNode := NewCell(x, nil)
	if q.size == 0 {
		q.front = newNode
		q.rear = newNode
	} else {
		q.rear.next = newNode
		q.rear = newNode
	}
	q.size++
}

func (q *Queue) PopLeft() (*State, bool) {
	if q.size == 0 {
		return nil, false
	} else {
		x := q.front.item
		q.front = q.front.next
		q.size--
		if q.size == 0 {
			q.rear = nil
		}
		return x, true
	}
}

func (q *Queue) IsEmpty() bool {
	return q.size == 0
}

/***********  end Queue  ***********/

type EdgeSorter struct {
    edges []Edge
    lessfunc []lessFunc
    used int
    length int
}

type lessFunc func(i, j *Edge)bool

func (ES EdgeSorter) Len() int {
    return len(ES.edges)
}

func (ES EdgeSorter) Swap(i, j int) {
    ES.edges[i], ES.edges[j] = ES.edges[j], ES.edges[i]
}

func (ES EdgeSorter) Less(i, j int) bool {
    var k int
    p, q := &ES.edges[i], &ES.edges[j]
    for k=0; k<len(ES.lessfunc)-1;k++ {
        less := ES.lessfunc[k]
        switch {
            case less(p, q):
                return true
            case less(q, p):
                return false
        }
    }
    return ES.lessfunc[k](p, q)
}

/*********** PriorityQueue ***********/
/*
type PriorityQueue struct {
    arr []*State
    size int
}

func (pq PriorityQueue) Len() int {
    return len(pq.arr)
}

func (pq PriorityQueue) Swap(i, j int) {
    pq.arr[i], pq.arr[j] = pq.arr[j], pq.arr[i]
}

func (pq PriorityQueue) Less(i, j int) bool{
    return pq.arr[i].time < pq.arr[j].time
}

func (pq *PriorityQueue) Push(x interface{}) {
    item := x.(*State)
    pq.arr = append(pq.arr, item)
    pq.size++
}

func (pq *PriorityQueue) Pop() interface{} {
    n := pq.size
    item := pq.arr[n - 1]
    pq.arr = pq.arr[:n - 1]
    pq.size--
    return item
}
*/


func main() {
    sc := bufio.NewScanner(os.Stdin)
    sc.Split(bufio.ScanWords)
	n, m := scanInt(sc), scanInt(sc)
	edges := make([]EdgeSorter, 0)
	for i := 0; i < n; i++ {
		edges = append(edges, EdgeSorter{})
	}
	for i := 0; i < m; i++ {
        a, b, c := scanInt(sc) - 1, scanInt(sc) - 1, scanInt(sc)
		edges[a].edges = append(edges[a].edges, Edge{to: b, newTime: c})
	}

    byNewTime := func(p1 *Edge, p2 *Edge) bool{
        return p1.newTime >= p2.newTime
    }

    for i, _ := range edges {
        v := &edges[i]
        v.lessfunc = append(v.lessfunc, byNewTime)
        sort.Sort(v)
        v.used = 0
        v.length = len(v.edges)
    }
    var minTime [100000]int
    for i := 0; i < n; i++ {
        minTime[i] = 2000000000
    }
    minTime[0] = 0
    que := Queue{}
    que.Push(&State{node: 0, time: 0})
	ans := -1
	for !que.IsEmpty() {
		state, _ := que.PopLeft()
		for edges[state.node].used < edges[state.node].length {
            e := edges[state.node].edges[edges[state.node].used]
			if e.newTime >= state.time {
                if e.to == n - 1 && e.newTime > ans {
                    ans = e.newTime
             

C++: #include <stdio.h>
#include <cmath>
#include <algorithm>
#include <cfloat>
#include <stack>
#include <queue>
#include <vector>
#include <string>
#include <iostream>
#include <set>
#include <map>
typedef long long int ll;
typedef unsigned long long int ull;
#define BIG_NUM 2000000000
#define MOD 1000000007
#define EPS 0.000000001
using namespace std;

struct Info{
	Info(int arg_to,int arg_time){
		to = arg_to;
		time = arg_time;
	}
	int to,time;
};

struct Data{
	Data(int arg_node_id,int arg_current_time){
		node_id = arg_node_id;
		current_time = arg_current_time;
	}
	bool operator<(const struct Data &arg) const{
		return current_time > arg.current_time;
	}
	int node_id,current_time;
};

vector<Info> V[100000];
int min_time[100000];

int main(){

	int N,M;
	scanf("%d %d",&N,&M);

	int from,to,time;
	for(int i = 0; i < M; i++){
		scanf("%d %d %d",&from,&to,&time);
		from--;
		to--;
		V[from].push_back(Info(to,time));
	}

	for(int i = 0; i < N; i++)min_time[i] = BIG_NUM;

	min_time[0] = 0;

	priority_queue<Data> Q;
	Q.push(Data(0,0));

	int ans = -1;

	while(!Q.empty()){

		if(Q.top().node_id == N-1){
			ans = max(ans,Q.top().current_time);
			Q.pop();
		}else if(Q.top().current_time > min_time[Q.top().node_id]){
			Q.pop();
		}else{


			for(int i = 0; i < V[Q.top().node_id].size(); i++){
				if(Q.top().current_time > V[Q.top().node_id][i].time)continue;

				if(min_time[V[Q.top().node_id][i].to] > V[Q.top().node_id][i].time){
					min_time[V[Q.top().node_id][i].to] = V[Q.top().node_id][i].time;
					Q.push(Data(V[Q.top().node_id][i].to,V[Q.top().node_id][i].time));
				}
			}
			Q.pop();
		}
	}

	printf("%d\n",ans);

	return 0;
}

C++: #include<iostream>
#include<utility>
#include<vector>
#define loop(i,a,b) for(int i=a;i<b;i++)
#define rep(i,a) loop(i,0,a)
#define pb push_back
using namespace std;
typedef long long ll;
typedef pair<int,ll> p;
vector<p> dist[100000];
bool used[100000];
int g;
int n,m,a,b;

ll dfs(int i,int pre){
	ll res=-1;
	if(i==g){
		rep(p,dist[pre].size()){
			if(dist[pre][p].first==i)return dist[pre][p].second;
		}
	}
	else{
		int predist=0;
		if(i!=0)rep(p,dist[pre].size())if(dist[pre][p].first==i)predist=dist[pre][p].second;
		rep(e,dist[i].size()){
			if(!used[dist[i][e].first]){
				if(predist>dist[i][e].second)continue;
				used[dist[i][e].first]=true;
				res=max(res,dfs(dist[i][e].first,i));
				used[dist[i][e].first]=false;
			}
		}
	}
	return res;
}

int main(){
	ll c;
	cin>>n>>m;
	rep(i,m){
		cin>>a>>b>>c;
		dist[a-1].pb(p(b-1,c));
	}
	g=n-1;
	rep(i,n)used[i]=false;
	used[0]=true;
	cout<<dfs(0,0)<<endl;
	return 0;
}

C++: #include <cstdio>
#include <cstring>
#include <vector>
#include <queue>
#include <string>
#include <algorithm>
#include <iostream>
#include <string>
#include <map>
#include <set>
#include <functional>
#include <iostream>
#define INF 1000000009
using namespace std;
typedef long long ll;
typedef pair<int,int> P;

int n,m;
vector<P> G[100001];
int dist[100001];

int dijk(){
	priority_queue<P,vector<P>,greater<P> > que;
	que.push(P(0,0));
	for(int i=0;i<n-1;i++){
		dist[i]=INF;
	}
	int res=-1;
	dist[0]=0;
	while(que.size()){
		P p=que.top();
		que.pop();
		int v=p.second,c=p.first;
		if(dist[v]<c)continue;
		for(int i=0;i<G[v].size();i++){
			P nex=G[v][i];
			int nev=G[v][i].first,nec=G[v][i].second;
			if(nec<c)continue;
			if(nev==n-1){
				res=max(res,nec);
			}else if(dist[nev]>nec){
				dist[nev]=nec;
				que.push(P(nec,nev));
			}
		}
	}
	return res;
}

int main(void){
	scanf("%d%d",&n,&m);
	for(int i=0;i<m;i++){
		int a,b,c;
		scanf("%d%d%d",&a,&b,&c);
		a--;
		b--;
		G[a].push_back(P(b,c));
	}
	printf("%d\n",dijk());
	return 0;
}