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 <cstdio>
#include <cstdlib>
#include <cmath>
#include <cstring>

#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <queue>
#include <stack>
#include <map>
#include <set>

#include <functional>
#include <cassert>

typedef long long ll;
using namespace std;

#define debug(x) cerr << #x << " = " << x << endl;


#define mod 1000000007 //1e9+7(prime number)
#define INF 1000000000 //1e9
#define LLINF 2000000000000000000LL //2e18
#define SIZE 100010


int main(){
  int n,m;
  int a,b,c;
  vector<pair<int,int> > way[SIZE];
  vector<pair<int,int> > ton;
  
  scanf("%d%d",&n,&m);

  for(int i=0;i<m;i++){
    scanf("%d%d%d",&a,&b,&c);
    a--; b--;
    if(a > b) swap(a,b);

    if(b == n-1){
      ton.push_back({a,c});
    }else{
      way[a].push_back({b,c});
      way[b].push_back({a,c});
    }
  }

  priority_queue<pair<int,int> > pq;
  bool visited[SIZE] = {};
  int memo[SIZE] = {};
  
  pq.push({0,0});

  while(pq.size()){
    pair<int,int> p = pq.top();
    pq.pop();

    if(visited[p.second]) continue;
    visited[p.second] = true;
    memo[p.second] = -p.first;

    for(int i=0;i<way[p.second].size();i++){
      if(-p.first <= way[p.second][i].second)
        pq.push({-way[p.second][i].second,way[p.second][i].first});
    }
  }

  int ans = -INF;
  
  for(int i=0;i<ton.size();i++){
    if(visited[i] && memo[ton[i].first] <= ton[i].second){
      ans = max(ans,ton[i].second);
    }
  }

  if(ans == -INF)
    puts("-1");
  else
    printf("%d\n",ans);
  
  return 0;
}

C++: #include <bits/stdc++.h>
#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,b) FOR(i,0,b)
#define PB push_back
#define ALL(c) c.begin(),c.end()
#define int LL
using namespace std;
typedef long long LL;
typedef int ut;
typedef pair<ut,ut> pr;
typedef vector<ut> VI;
typedef vector<pr> Vpr;
typedef priority_queue<pr,Vpr,greater<pr> > PQ;
const int SIZE=3*1e5;
const ut INF=1LL<<60;
Vpr edge[SIZE];
int N,M,a,b,c;
int reach[SIZE];
int dijkstra(){
	PQ qu;
	qu.push(pr(0,1));
	while(!qu.empty()){
		int now=qu.top().second,times=qu.top().first;
		qu.pop();
	//	cout << now <<" " << times << endl;
		if(reach[now]<times) continue;
		REP(i,edge[now].size()){
			int next=edge[now][i].first;
			int nextT=edge[now][i].second;
			if(nextT<times) continue;
			if(next==N){
				reach[next]=max(reach[next],nextT);
				continue;
			}
			if(nextT>=reach[next]) continue;
			
			reach[next]=nextT;
			qu.push(pr(nextT,next));
		}
	}
	return reach[N];
}
signed main(){
	cin.tie(0);
	cin >> N >> M;
	FOR(i,1,N+1){
		reach[i]=INF;
	}
	reach[N]=-1;
	reach[1]=0;
	REP(i,M){
		cin >> a >> b >> c;
		edge[a].PB(pr(b,c));
		edge[b].PB(pr(a,c));
	}
	cout << dijkstra() << endl;
	return 0;
}