#include <iostream>
#include <cstdio>
#include <vector>
#include <cstring>
#include <queue>
#include <cstdlib>
#define DN 250005
#define pb push_back
#define mp make_pair
#define f first
#define s second
#define un unsigned
using namespace std;

int minim[DN],maxc;
vector<pair<int,int> > list[DN];
vector<int> v[1024];


FILE *in,*out;


void read(int &n,int &m,int &x,int &y)
{
    in=fopen("pscnv.in","rb");
    int ind=0,count=0,a,b,c;
    long lsize;
    char * buffer;
    size_t result;

    fseek(in,0,SEEK_END);
    lsize=ftell(in);
    rewind(in);
    buffer=(char*) malloc(sizeof(char)*lsize);
    result=fread(buffer,1,lsize,in);

    for(int i=0;i<lsize;++i)
    {
        if(isdigit(buffer[i]))
        {
            int nr=0;
            while(isdigit(buffer[i]))
            {
                nr=nr*10+buffer[i]-'0';
                ++i;
            }
            ++ind;
            if(ind==1) n=nr;
                else if(ind==2) m=nr;
                    else if(ind==3) x=nr;
                        else if(ind==4) y=nr;
                            else
                            {
                                ++count;
                                if(count==1) a=nr;
                                    else
                                        if(count==2) b=nr;
                                            else c=nr;

                                if(count==3)
                                {
                                    list[a].pb(mp(b,c));
                                    maxc=max(maxc,c);
                                    count=0;
                                }
                            }
        }
    }


}

void expand(int nod)
{
    for(un int i=0;i<list[nod].size();++i)
    {
        int next_nod=list[nod][i].f;
        int cost=list[nod][i].s;
        if(minim[next_nod] > max(cost,minim[nod]) )
        {
            minim[next_nod]=max(cost,minim[nod]);
            v[max(cost,minim[nod])].pb(next_nod);
        }
    }

}


int main()
{
    int n,m,x,y;
    out=fopen("pscnv.out","w");
    read(n,m,x,y);

    memset(minim,127,sizeof(minim));

    minim[x]=0;
    expand(x);
    for(int i=1;i<=maxc;++i)
        for(int j=0;j<v[i].size();++j)
        {
            if(v[i][j]==y)
            {
                fprintf(out,"%d",minim[y]);
                return 0;
            }
            if(minim[v[i][j]]==i)
                expand(v[i][j]);
        }

    return 0;
}