#include<cstdio>
#include<queue>
#include<vector>
using namespace std;
const int NMAX = 250009;
const int INF = 1 << 30;

vector< pair<int,int> > v[NMAX];
queue< int > coada;
int n,m,sol[NMAX],x,y,viz[NMAX],lungime;

void read()
{
    freopen("pscnv.in","r",stdin);
    scanf("%d%d%d%d",&n,&m,&x,&y);
    int a ,b,c;
    char sir[30],*p;
    for(int i = 1 ; i <= m ; i++){
        fgets(sir,30,stdin);
        a = b = c = 0;
        for(p = sir ; *p <= '9' && *p >= '0' ; p++) a= a*10 + (*p-48);
        p++;
        for(; *p <= '9' && *p >= '0' ; p++) b= b*10 + (*p-48);
        p++;
        for(; *p <= '9' && *p >= '0' ; p++) c= c*10 + (*p-48);
        v[a].push_back(make_pair(b,c));
    }
    for(int i = 1 ; i <= n ; i++)
        if(i != x)
            sol[i] = INF;

}

int bmf(int start)
{

    sol[start] = 0;
    coada.push(start);
    viz[start] = 1;
    int i,k,vecin;
    while( !coada.empty() )
    {

        k = coada.front();
        viz[k] = 0;
        for(i = 0 ; i < v[k].size() ; i++){

            vecin = v[k][i].first;
            if(sol[vecin] > max(v[k][i].second,sol[k])){
                sol[vecin] = max(v[k][i].second,sol[k]);
                if(!viz[vecin]){
                    coada.push(vecin);
                    viz[vecin] = 1;
                }
            }
        }
        coada.pop();
    }
    return sol[y];
}

int main()
{
    freopen("pscnv.out","w",stdout);
    read();
    printf("%d",bmf(x));
    return 0;
}