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 FOR(i,a,b) for(int i=a;i<b;i++)
#define REP(i,b) FOR(i,0,b)
#define MP make_pair
#define PB push_back

using ll=long long;
using pii=pair<int,int>;
using vi=vector<int>;

int read(){
	int i;
	scanf("%d",&i);
	return i;
}

struct Edge{
	int a,b;
};

bool used[114514],cur[114514];
vi g[114514];

int main(){
	int n=read(),m=read();
	map<int,vector<Edge>> es;
	REP(i,m){
		int a=read()-1,b=read()-1,t=read();
		es[t].PB(Edge{a,b});
	}
	int ans=-1;
	cur[0]=true;
	for(auto kv:es){
		queue<int> q;
		for(auto e:kv.second){
			g[e.a].PB(e.b);
			if(cur[e.a]&&!used[e.a]){
				used[e.a]=true;
				q.push(e.a);
			}
		}
		while(!q.empty()){
			int v=q.front();q.pop();
			for(auto u:g[v])if(!cur[u]){
				cur[u]=true;
				q.push(u);
			}
		}
		for(auto e:kv.second){
			g[e.a].clear();
			used[e.a]=false;
		}
		if(cur[n-1]){
			ans=kv.first;
			cur[n-1]=false;
		}
	}
	cout<<ans<<endl;
}

C++: #include <iostream>
#include <vector>
#define	to first
#define co second
using namespace	std;
int n,m,r,flag[100000];
vector <pair<int,int> > side[100000];
void dfs(int where,int time){
  if(flag[where]) return;
  flag[where]=1;
  if(where==n-1) r=max(r,time);
  for(int i=0;i<side[where].size();i++)
    if(side[where][i].co>=time)
      dfs(side[where][i].to,side[where][i].co);
  flag[where]=0;
}
int main(){
  cin>>n>>m;
  for(int i=0,a,b,c;i<m;i++){
    cin>>a>>b>>c;
    side[a-1].push_back(make_pair(b-1,c));
  }
  dfs(0,0);
  if(!r) cout<<-1<<endl;
  else cout<<r<<endl;
  return 0;
}

C++: #include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;

typedef int _loop_int;
#define REP(i,n) for(_loop_int i=0;i<(_loop_int)(n);++i)
#define FOR(i,a,b) for(_loop_int i=(_loop_int)(a);i<(_loop_int)(b);++i)
#define FORR(i,a,b) for(_loop_int i=(_loop_int)(b)-1;i>=(_loop_int)(a);--i)

#define DEBUG(x) cout<<#x<<": "<<x<<endl
#define DEBUG_VEC(v) cout<<#v<<":";REP(i,v.size())cout<<" "<<v[i];cout<<endl
#define ALL(a) (a).begin(),(a).end()

#define CHMIN(a,b) a=min((a),(b))
#define CHMAX(a,b) a=max((a),(b))

// mod
const ll MOD = 1000000007ll;
#define FIX(a) ((a)%MOD+MOD)%MOD

// floating
typedef double Real;
const Real EPS = 1e-11;
#define EQ0(x) (abs(x)<EPS)
#define EQ(a,b) (abs(a-b)<EPS)
typedef complex<Real> P;

int n,m;
int dist[125252];
vector<pii> g[125252];

const int INF = 830252521;

int main(){
  scanf("%d%d",&n,&m);
  REP(i,m){
    int a,b,c;
    scanf("%d%d%d",&a,&b,&c);
    --a;--b;
    g[a].push_back(pii(b,c));
    g[b].push_back(pii(a,c));
  }
  // dijkstra in 0~n-2
  REP(i,n)dist[i] = INF;
  priority_queue<pii> Q;
  Q.push(pii(-0,0));
  dist[0] = 0;
  while(!Q.empty()){
    pii P = Q.top(); Q.pop();
    int d = -P.first;
    int pos = P.second;
    if(dist[pos]<d)continue;
    REP(i,g[pos].size()){
      int to = g[pos][i].first;
      if(to==n-1)continue;
      int c = g[pos][i].second;
      if(c<d)continue;
      if(c>=dist[to])continue;
      dist[to] = c;
      Q.push(pii(-c,to));
    }
  }
  int ans = -1;
  REP(i,n){
    REP(j,g[i].size()){
      int to = g[i][j].first;
      if(to!=n-1)continue;
      int c = g[i][j].second;
      if(c>=dist[i]){
        CHMAX(ans,c);
      }
    }
  }
  printf("%d\n",ans);
  return 0;
}