#include <iostream>
#include <fstream>
#include <vector>

using namespace std;

struct muchie{
    int nod,dist;
};

vector <muchie> graf[30001];
ifstream f("sate.in");
ofstream g("sate.out");
int n,m,nodinit,nodfin,minim,d[30001];
int stnod[30001],stdist[30001],k,curr;

/*void dfs(int nod,int dist)
{
    int i;
    if(nod==nodfin) {if((!minim) || (dist<minim)) minim=dist;}
    else if(!d[nod])
            {
                d[nod]=1;
                for(i=0;i<graf[nod].size();i++)
                    {
                        dfs(graf[nod][i].nod,dist+graf[nod][i].dist);
                    }
            }
}*/

int main()
{   int x,y,dis,i;

    f>>n>>m>>nodinit>>nodfin;

    for(i=1;i<=m;i++)
    {
        f>>x>>y>>dis;

        graf[x].push_back({y,dis});
        graf[y].push_back({x,-dis});
    }

    curr=1;
    k=1;
    stnod[k]=nodinit;
    stdist[k]=0;
    d[nodinit]=1;

    while(curr<=k)
    {
        if(stnod[curr]==nodfin) if((!minim) || (stdist[curr]<minim)) minim=stdist[curr];
        for(i=0;i<graf[stnod[curr]].size();i++)
            if(!d[graf[stnod[curr]][i].nod])
        {   d[graf[stnod[curr]][i].nod]=1;
            k++;
            stnod[k]=graf[stnod[curr]][i].nod;
            stdist[k]=stdist[curr]+graf[stnod[curr]][i].dist;
        }
        curr++;
    }

    //dfs(nodinit,0);

    g<<minim;

    return 0;
}