#include <iostream>
#include<fstream>
#include<vector>
#include<fstream>
#include<algorithm>
#include<cmath>
#define Nmax 20000002
typedef int coada[30001];
using namespace std;
ifstream f("sate.in");
ofstream g("sate.out");
int a,p,cst[30001],n,m,x,y,i,j,cost,q,k,l;
coada c;
bool ok;
vector<pair <int,int> >v[30001];
inline void BFS(int nod)
{
    cst[nod]=0;
    int siz=1,start=1;
    c[start]=nod;
    while(siz>=start)
    {
        int k=c[start];
        for(int i=0;i<v[k].size();i++)
            if(cst[v[k][i].first]>cst[k]+v[k][i].second)
        {
            cst[v[k][i].first]=cst[k]+v[k][i].second;
            siz++;
            c[siz]=v[k][i].first;
        }
        start++;
    }
}
int main()
{
    f>>n>>m>>x>>y;
    for(q=1;q<=m;q++)
    {
        f>>i>>j>>cost;
        v[i].push_back(make_pair(j,cost));
        v[j].push_back(make_pair(i,cost));
        for(k=0;k<v[i].size()-1;k++)
            for(l=1;l<v[i].size();l++)
        {
            int p=v[i][k].first;bool ok=1;
            for(a=0;a<v[p].size() && ok;a++)
                if(v[p][a].first==v[i][l].first) ok=0;
            if(ok)
            {v[v[i][k].first].push_back(make_pair(v[i][l].first,abs( v[i][k].second-v[i][l].second )));
            v[v[i][l].first].push_back(make_pair(v[i][k].first,abs( v[i][k].second-v[i][l].second )));}
        }
            p=v[j][k].first;ok=1;
            for(a=0;a<v[p].size() && ok;a++)
                if(v[p][a].first==v[j][l].first)
                    ok=0;

        for(k=0;k<v[j].size()-1;k++)
            for(l=1;l<v[j].size();l++)
        {
            p=v[j][k].first;ok=1;
            for(a=0;a<v[p].size() && ok;a++)
                if(v[p][a].first==v[j][l].first)
                    ok=0;
            if(ok)
            {v[v[j][k].first].push_back(make_pair(v[j][l].first,abs( v[j][k].second-v[j][l].second )));
            v[v[j][l].first].push_back(make_pair(v[j][k].first,abs( v[j][k].second-v[j][l].second )));}
        }
    }
    for(i=1;i<=n;i++)
        cst[i]=Nmax;
    BFS(x);
    g<<cst[y];
    return 0;
}