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<bits/stdc++.h>
using namespace std;
#define MAX_N 100000
struct edge{ int to,cost; };
typedef pair<int,int> P;
const int INF=1000000001;

int N,M;
int d[MAX_N];
vector<edge> G[MAX_N];

int main(){
  cin>>N>>M;
  for(int i=0;i<M;i++){
    int a,b,c;
    scanf("%d %d %d",&a,&b,&c);
    G[a].push_back((edge){b,c});
  }
  int ans=-1;  
  priority_queue< P , vector<P> , greater<P> > Q;
  fill(d,d+MAX_N,INF);
  Q.push(P(1,1));
  d[1]=1;
  while(!Q.empty()){
    P p=Q.top();Q.pop();
    int pos=p.second;
    int cost=p.first;
    if(d[pos]<cost)continue;
    for(int i=0;i<(int)G[pos].size();i++){
      edge e=G[pos][i];
      if(e.cost<d[pos])continue;
      if(e.to==N)ans=max(ans,e.cost);
      if(d[e.to]>e.cost){
        d[e.to]=e.cost;
        Q.push(P(d[e.to],e.to));
      }
    }
  }
  printf("%d\n",ans);
  return 0;
}

C++: #include<iostream>
#include<vector>
using namespace std;
#define loop(i,a,b) for(int i=a;i<b;i++)
#define rep(i,a) loop(i,0,a)
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<vvi> vvvi;
typedef pair<int,int> pii;
typedef vector<pii> vp;
typedef vector<vp> vvp;
const int inf=2e9;
#define pb push_back
int main(){
  int n,m;
  cin>>n>>m;
  //  vvvi cost(n,vvi(n));
  vvp cost(n);
  //  rep(i,n)cost[i][n-1]=-1;
  rep(i,m){
    int a,b,c;
    cin>>a>>b>>c;
    a--;b--;
    cost[a].pb(pii(b,c));
    //    cost[a][b].pb(c);
    //    if(b==n-1)cost[a][b]=max(cost[a][b],c);
    //else cost[a][b]=min(cost[a][b],c);
  }
  vi used(n);
  vi d(n,inf);
  d[0]=0;
  used[n-1]=true;
  while(1){
    int v=-1;
    rep(i,n)if(!used[i]&&(v==-1||d[i]<d[v]))v=i;
    if(v==-1)break;
    used[v]=true;
    rep(i,cost[v].size())if(d[v]<=cost[v][i].second&&d[cost[v][i].first]>cost[v][i].second)d[cost[v][i].first]=cost[v][i].second;
    // rep(i,n-1)rep(j,cost[v][i].size())if(d[v]<=cost[v][i][j]&&d[i]>cost[v][i][j])d[i]=cost[v][i][j];
  }
  int out=-1;
  rep(i,n-1)rep(j,cost[i].size())if(cost[i][j].first==n-1&&d[i]<=cost[i][j].second)out=max(out,cost[i][j].second);
  //  rep(i,n-1)rep(j,cost[i][n-1].size())if(d[i]<=cost[i][n-1][j])out=max(out,cost[i][n-1][j]);
  cout<<out<<endl;
  //rep(i,n)cout<<d[i]<<endl;
}

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(); //[-time,place]
    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[ton[i].first] && 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;
}