#include <iostream>
#include <queue>
#include <vector>
#include <stdio.h>

using namespace std;

#define nmax 250000
#define mp make_pair
#define f first
#define s second
#define pb push_back

const int inf = 1e9;

vector <int> d[2100];
vector <pair<int,int> > v[nmax];
int ans[nmax];
int n,m,i,a,b,x,y,cost,j,k;

#define DIM 10000
char buff[DIM];
int poz=0;

void citeste(int &numar)
{
     numar = 0;
     //cat timp caracterul din buffer nu e cifra ignor
     while (buff[poz] < '0' || buff[poz] > '9')
          //daca am "golit" bufferul atunci il umplu
          if (++poz == DIM)
               fread(buff,1,DIM,stdin),poz=0;
     //cat timp dau de o cifra recalculez numarul
     while ('0'<=buff[poz] && buff[poz]<='9')
     {
          numar = numar*10 + buff[poz] - '0';
          if (++poz == DIM)
               fread(buff,1,DIM,stdin),poz=0;
     }
}

int main()
{
    freopen("pscnv.in","r",stdin);
    freopen("pscnv.out","w",stdout);
    citeste(n);
    citeste(m);
    citeste(a);
    citeste(b);
    for(i=1; i<=m; ++i)
    {
        citeste(x);
        citeste(y);
        citeste(cost);
        v[x].push_back(mp(cost,y));
    }
    for(i=1; i<=n; ++i)
        ans[i]=inf;
    ans[a]=0;
    d[0].pb(a);
    for(i=0; i<=1000 && i<ans[b]; ++i)
    {
        for(j=0; j<d[i].size(); ++j)
        if(ans[d[i][j]]==i)
        {
            int nod = d[i][j];
            for(k=0; k<v[nod].size(); ++k)
            {
                if(max(v[nod][k].f,i)<ans[v[nod][k].s])
                {
                    ans[v[nod][k].s]=max(v[nod][k].f,i);
                    d[ans[v[nod][k].s]].pb(v[nod][k].s);
                }
            }
        }
    }
    cout<<ans[b];
}