#include <cstdio>
#include <vector>
#include <string>
#include <algorithm>
#include <fstream>
#define INF 25000000
using namespace std;
FILE *f,*g;
struct cp{int y,c; }ax;
vector <cp> b[30200];
int n,m,st,dr;
int D[30200];
vector <int>q ;

inline cp mkcp(int a,int b){
    cp ax;
    ax.y=a;
    ax.c=b;
    return ax;
}

void read()
{
    int i,x,y,z;
    ifstream fin("sate.in");
    g=fopen("sate.out","w");

    fin>>n>>m>>st>>dr;
    if (st>dr) swap(st,dr);

    for (i=1;i<=m;i++)
    {
        fin>>x>>y>>z;
        if (x<y)
        {
            b[x].push_back(mkcp(y,z));
            b[y].push_back(mkcp(x,-z));
        }
        else
        {
            b[x].push_back(mkcp(y,-z));
            b[y].push_back(mkcp(x,z));
        }

    }
}




void dijkstra()
{
    int i,j,x;

    for (i=1;i<=n;i++)
    {
        D[i]=INF;
    }
    D[st]=0;

    q.push_back(st);


    for (i=0;i<q.size();i++)
    {
        x=q[i];

        for (j=0;j<b[x].size();j++)
            if (D[b[x][j].y]==INF)
            {
                D[b[x][j].y]=b[x][j].c+D[x];
                if (b[x][j].y==dr) return ;
                q.push_back(b[x][j].y);
            }
    }


}



int main()
{
    read();
    dijkstra();

    fprintf(g,"%d",D[dr]);

	return 0;
}