#include <cstdio>
#include <vector>
#include <string>
#include <algorithm>
#define INF 25000000
using namespace std;
FILE *f,*g;
struct cp{int y,c; }ax;
vector <cp> a[30200],b[30200];
int n,m,st,dr;
int D[30200];
struct cp2{int x,y,z;} M[100100];
vector <int>q ;



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

bool cmp(cp2 a, cp2 b){
   if (a.x!=b.y)
    return a.x<b.x;
    return a.y<=b.y;
}


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

    fscanf(f,"%d%d%d%d",&n,&m,&st,&dr);
    if (st>dr) swap(st,dr);

    for (i=1;i<=m;i++)
    {
        fscanf(f,"%d%d%d",&M[i].x,&M[i].y,&M[i].z);
    }

    stable_sort(M+1,M+m+1,cmp);

    for (i=1;i<=m;i++)
        a[M[i].x].push_back(mkcp( M[i].y,M[i].z));


}

void solve()
{
    int i,j,d,x;

    for (i=1;i<=n;i++)
        if (a[i].size()>0)
        {
            for (j=0,d=0,x=i;j<a[i].size();j++)
            {
                b[x].push_back(mkcp(a[i][j].y,a[i][j].c-d));
                b[a[i][j].y].push_back(mkcp(x,-(a[i][j].c-d)));
                d=a[i][j].c;
                x=a[i][j].y;
            }
        }

}


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();
    solve();
    dijkstra();

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

	return 0;
}