#include<fstream>
#include<vector>
#include<cstring>
#include<queue>
#define NMAX 250010

using namespace std;

ifstream f("pscnv.in");
ofstream g("pscnv.out");

struct muchie
{
    int nod, cost;
}r;
vector<muchie> v[NMAX];

char c[NMAX], *p;
int n, m, X, Y, lim=-1, vz[NMAX], q[NMAX];

int next_int()
{
    int nr=0;

    while (*p>='0' && *p<='9')
    {
        nr=nr*10+(*p)-'0';
        ++p;
    }

    ++p;

    return nr;
}

void Citeste()
{
    int i, x;

    f.getline(c, NMAX); p=c;

    n=next_int(); m=next_int(); X=next_int(); Y=next_int();

    for (i=1; i<=m; ++i)
    {
        f.getline(c, NMAX); p=c;

        x=next_int(); r.nod=next_int(); r.cost=next_int();

        v[x].push_back(r); lim=max(lim, r.cost);
    }
}

inline int posibil(int val)
{
    int p=1, u=1, nod, i;
    muchie r;

    memset(vz, 0, sizeof(vz));
    q[1]=X; vz[X]=1;

    while (p<=u && !vz[Y])
    {
        nod=q[p];

        ++p;

        for (i=0; i<v[nod].size(); ++i)
        {
            r=v[nod][i];

            if (!vz[r.nod] && r.cost<=val)
            {
                vz[r.nod]=1;
                q[++u]=r.nod;
            }
        }
    }

    return vz[Y];
}

void Solve()
{
    int st=1, dr=lim, mij, pz=lim;

    while (st<=dr)
    {
        mij=(st+dr)>>1;

        if ( posibil(mij) )
        {
            dr=mij-1;
            pz=mij;
        }
        else st=mij+1;
    }

    g<<pz<<"\n";
}

int main()
{
    Citeste();

    Solve();

    f.close();
    g.close();
    return 0;
}