#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

const int inf = 1e9;

priority_queue <pair<int,int> , vector <pair<int,int> >, greater <pair<int,int> > >h;
vector <pair<int,int> > v[nmax];
int ans[nmax];
int n,m,i,a,b,x,y,cost;

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;
    h.push(mp(0,a));
    while(h.size() && h.top().f<ans[b])
    {
        int nod = h.top().s;
        h.pop();
        for(i=0; i<v[nod].size(); ++i)
            if(max(v[nod][i].f,ans[nod])<ans[v[nod][i].s])
            {
                ans[v[nod][i].s]=max(v[nod][i].f,ans[nod]);
                h.push(mp(ans[v[nod][i].s],v[nod][i].s));
            }
    }
    fout<<ans[b];
}