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

#define NEK 1000000000

int d[10002];
int p[10002];

int hash[11000];

struct tab {
	int uod, udo, del;
} tb[50002];

int fronta[100000];
int frend;
int frbeg;


int N,M,S,C;

int qcmp(const void *a, const void *b) {
	int *x= (int*)a, *y=(int*)b;
	if(d[*x] < d[*y]) return -1;
	if(d[*x] > d[*y]) return 1;
	return 0;
}

void priority() {
	for(int i=0; i<frbeg; i++) {
		fronta[i] = 10001;
	}
	qsort(fronta, frend, sizeof(int), qcmp);
	frend -= frbeg;
	frbeg = 0;

	for(int i=0; i<frend; i++) {
		printf("%d [%d]\n",fronta[i], d[fronta[i]]);
	} printf("------");
}

void init_queue(void) {
	frbeg = frend = 0;
}

void enqueue(int u) {
	fronta[frend] = u;
	frend++;

	int i = frend-1;
	while( (i>frbeg) && (d[fronta[i-1]] > d[u]) ) {
		fronta[i] = fronta[i-1];
		fronta[i-1] = u;
	}
}

void fixpri(int x) {
	int tmp;
	while( (x>frbeg) && (d[fronta[x-1]] > d[fronta[x]]) ) {
		tmp = fronta[x-1];
		fronta[x-1] = fronta[x];
		fronta[x] = tmp;
		x--;
	}
}
		
int dequeue(void) {
	int x = fronta[frbeg];
	frbeg++;
	return x;
}

bool isempty(void) {
	return frbeg == frend;
}

int w(int u, int v) {
	int i = hash[u];
	while( (tb[i].uod == u) && (tb[i].udo != v) ) i++;
	return (tb[i].udo == v) ? tb[i].del : NEK;
}

void init_paths(void) {
	for(int i=0; i<=N; i++) {
		d[i] = NEK;
		p[i] = 0;
	}
	d[S] = 0;
}

void relax(int u, int v) {
	int ww = w(u,v);
	if( d[v] > (d[u]+ww) ) {
		d[v] = d[u] + ww;
		p[v] = u;
	}
}

void makehash(void) {
	for(int i = M; i>0; i--) {
		hash[tb[i].uod] = i;
	}
}

int cmp(const void *a, const void *b) {
	if( ((tab*)a)->uod < ((tab*)b)->uod) return -1;
	if( ((tab*)a)->uod > ((tab*)b)->uod) return 1;
	
	return 0;
}

bool closed[10001];

int main(void) {
	d[10001] = NEK+1;
	
	do {
		scanf("%d %d %d %d", &N, &M, &S, &C);
		if( (N | M | S | C) == 0 ) return 0;

		for(int	i=1; i<=M; i++) {
			scanf("%d %d %d", &tb[i].uod, &tb[i].udo, &tb[i].del);
		}
		
		if(S == C) {
			printf("0\n");
			continue;
		}
		
		//sort
		qsort(&tb[1], M, sizeof(tab), cmp);

		//make hash
		makehash();
	
		//b-f
		init_paths();
		init_queue();
		for(int i= 1; i<=N; i++) {
			enqueue(i);
			closed[i] = false;
		}
		priority();
		
		int u,z;
		
		while( !isempty() && !closed[C]) {
			u = dequeue();
			closed[u] = true;
			if(u == C) break;
			
			z = hash[u];
			while(tb[z].uod == u) {
				if(!closed[tb[z].udo]) relax(u,tb[z].udo);
				z++;
			}
			priority();
		}
		
		printf("%d\n",d[C]);
	} while (1);
}