#include <iostream>
#include <queue>
#include <vector>
#include <fstream>

using namespace std;

ifstream fin("pscnv.in");
ofstream fout("pscnv.out");

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

const int inf = 1e9;

vector <int> d[1010];
vector <pair<int,int> > v[nmax];
int ans[nmax];
int n,m,i,a,b,x,y,cost,j,k;

int main()
{
    fin>>n>>m>>a>>b;
    for(i=1; i<=m; ++i)
    {
        fin>>x>>y>>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)
        {
            int nod = d[i][j];
            if(ans[nod]==i)
            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);
                }
            }
        }
    }
    fout<<ans[b];
}