#include <stdio.h>
#include <queue>
#define Max 30010
using namespace std;

struct nod{
    int info;
    int D;
    nod *next;
};

int N,Y,X,M;
nod *G[Max];

void add(int a, int b, int d)
{
    nod *p = new nod;
    p->info = b;
    p->D = d;
    p->next = G[a];
    G[a] = p;
}

void read()
{
    int a, b, d;
    scanf("%d %d %d %d",&N,&M,&X,&Y);
    for(int i = 1; i <= M; i++)
    {
        scanf("%d %d %d",&a,&b,&d);
        add(a,b,d);
        add(b,a,-d);
    }
    if(X > Y)
    {
        int t = X;
        X = Y;
        Y = t;
    }
}

unsigned int cost[Max];

unsigned int BFS()
{
    int t;
    queue <int> Q;
    nod *p;
    Q.push(X);
    while(!Q.empty())
    {
        t = Q.front();
        p = new nod;
        for(p = G[t]; p; p = p->next)
            if(!cost[p->info])
            {
                Q.push(p->info);
                cost[p->info] = cost[t] + p->D;
            }
        if(cost[Y])
            return cost[Y];
        if(t == X)
            cost[X] = 1;
        Q.pop();
    }
    return 0;
}

int main()
{
    freopen ("sate.in","r",stdin);
    freopen ("sate.out","w",stdout);
    read();
    printf("%u\n",BFS());
    return 0;
}