#include <stdio.h>
#include <string.h>
#include <vector>

using namespace std;

#define mp make_pair
#define pb push_back
#define f first
#define s second
#define NMax 305
#define MMax 1505

int N, S[NMax], X[NMax * NMax], Y[NMax * NMax], cst[NMax * NMax], OPT[NMax][NMax], sA, sB;
vector< pair<int, int> > G[NMax];

int main(void)
{
	int M, u, v, D, i, j;
    vector< pair<int, int> >::iterator it;
    
	freopen("sate.in", "r", stdin);
    freopen("sate.out", "w", stdout);

    memset(OPT, 0, sizeof(OPT));

    scanf("%d %d %d %d", &N, &M, &sA, &sB);
    for (i = 1; i <= M; i++)
    {
    	scanf("%d %d %d", &u, &v, &D);

        X[i] = u; Y[i] = v; cst[i] = D;
    }

    for (i = 1; i <= M; i++)
     	for (j = 1; j <= M; j++)
       	if (i != j)
        {
            if (X[i] == X[j])
            {
            	if (Y[i] < Y[j] && !OPT[Y[i]][Y[j]])
                    M++, X[M] = Y[i], Y[M] = Y[j], cst[M] = cst[j] - cst[i],
                    OPT[Y[i]][Y[j]] = cst[M];
            	else if (Y[j] < Y[i] && !OPT[Y[j]][Y[i]])
                    M++, X[M] = Y[j], Y[M] = Y[i], cst[M] = cst[i] - cst[j],
                    OPT[Y[j]][Y[i]] = cst[M];
            }
            else if (Y[i] == Y[j])
            {
            	if (X[i] < X[j] && !OPT[X[i]][X[j]])
                    M++, X[M] = X[i], Y[M] = X[j], cst[M] = cst[i] - cst[j],
                    OPT[X[i]][X[j]] = cst[M];
                else if (X[j] < X[i] && !OPT[X[j]][X[i]])
                    M++, X[M] = X[j], Y[M] = X[i], cst[M] = cst[j] - cst[i],
                    OPT[X[j]][X[i]] = cst[M];
            }
            
            
        }
        
	for (i = 1; i <= M; i++)
        G[X[i]].pb( mp(Y[i], cst[i]) );


    for (S[1] = 0, i = 2; i <= N; i++) S[i] = -1;    

    for (i = 1; i <= N; i++)
    {
    	if (S[i] == -1) continue;
        
		for (it = G[i].begin(); it != G[i].end(); it++)
            S[it->f] = S[i] + it->s;
    }

    printf("%d\n", S[sB]-S[sA]);

	return 0;
}