#include <cstdio>
#include <algorithm>
#include <cstring>
#include <vector>
#include <queue>
#include <utility>
using namespace std;

char buff[1<<24];
int pos,sz,x,y,n,m;

vector< pair<int,int> > G[250001];

struct comp
{
    bool operator()(const pair<int,int>& a,const pair<int,int>& b)
    {
        return a.second > b.second;
    }
};

priority_queue< pair<int,int>, vector< pair<int,int> >, comp> Q;

int nextInt()
{
    int Ret = 0;
    while (!(buff[pos] >= '0' && buff[pos] <= '9')) ++pos;
    while (buff[pos] >= '0' && buff[pos] <= '9' && pos < sz)
    {
        Ret = Ret * 10 + buff[pos] - '0';
        pos++;
    }
    return Ret;
}

void read()
{
    fread(buff,1,1<<24,stdin);
    pos = 0; sz = strlen(buff);
}

int dist[250001];

void Dijkstra()
{
    memset(dist,0x3f3f3f3f,sizeof dist);
    Q.push(make_pair(x,-1));
    int u,d,nd;
    while (!Q.empty())
    {
        u = Q.top().first;
        d = Q.top().second;
        Q.pop();
        for (vector< pair<int,int> >::iterator it = G[u].begin(); it != G[u].end(); it++)
        {
            nd = max (d,it->second);
            if (dist[it->first] > nd)
            {
                dist[it->first] = nd;
                Q.push(make_pair(it->first,nd));
            }
        }
    }
}

int main()
{
    freopen("pscnv.in", "r", stdin);
    freopen("pscnv.out", "w", stdout);

    scanf("%d%d%d%d\n",&n,&m,&x,&y);

    read();
    for (int i = 1; i <= m; i++)
        G[nextInt()].push_back(make_pair(nextInt(),nextInt()));

    Dijkstra();

    printf("%d\n",dist[y]);
}