#include <stdio.h>
#include <stdlib.h>

#define FIN "sate.in"
#define FOUT "sate.out"
#define MAXN 30001
#define MAXM 100024

int n, m, x, y;

struct elem { int x, c; elem *r; } * L[MAXN];

void push(int a, int b, int c)
{
    elem *temp = new elem;
    temp->x = b; temp->c = c; temp->r = L[a];
    L[a] = temp;
}

void citire()
{
    int i, a, b, c;
    freopen(FIN, "r", stdin);
    freopen(FOUT, "w", stdout);
    scanf("%d%d%d%d", &n, &m, &x, &y);
    for (i=0; i<m; ++i) {
        scanf("%d %d %d", &a, &b, &c);
        push(a, b, c);
        push(b, a, -c);
    }
}

long long dist = 0;
struct ceva { int s; elem **tembel, *p, *last; } S[MAXM*5]; // well teoretic e *2 dar ..
int t = -1;

void fixme(int s)
{
    S[++t] = (ceva) { x, 0, L[s], 0 };
    while (S[t].s != y && t >= 0) {
        if (S[t].p) {
            if (t && S[t].p->x == S[t-1].s) {
                S[t].last = S[t].p, S[t].p = S[t].p->r;
                continue;
            }
            // eclipsam...
            S[t].tembel = S[t].last ? &S[t].last->r : &L[S[t].s];
            *S[t].tembel = S[t].p->r;
            //fprintf(stderr, "%d => %d (%d)\n", S[t].s, S[t].p->x, S[t].p->c);
            dist += S[t].p->c;
            // merg mai departe...
            S[t+1] = (ceva) { S[t].p->x, 0, L[ S[t].p->x ], 0 }; ++t;
            continue;
        }
        // ne intoarcem ...
        --t;
        dist -= S[t].p->c;
        *S[t].tembel = S[t].p;
        S[t].last = S[t].p, S[t].p = S[t].p->r;
    }
    printf("%lld\n", dist);
}

int main()
{
    citire();
    fixme(x);
    return 0;
}