#include <cstdio>

#define file_in "sate.in"
#define file_out "sate.out"

#define Nmax 101002

int n,m,q,w;
int x[5*Nmax];
int y[5*Nmax];
int c[5*Nmax];
int d[5*Nmax];

void citire()
{
	int i;
	freopen(file_in,"r",stdin);
	freopen(file_out,"w",stdout);
	
	scanf("%d %d %d %d", &n, &m, &q,&w);
	for (i=1;i<=m;++i)
	{
		scanf("%d %d %d", &x[i], &y[i], &c[i]);
		if (x[i]==q)
			d[y[i]]=c[i];
		if (y[i]==q)
			d[x[i]]=-c[i];
	}
}

void solve()
{
	int i;
	
	for (i=1;i<=n;++i)
		 if (i!=q)
			 if (d[i]==0)
				 d[i]=0x3f3f3f3f;
	
	int ok=1;
	while(ok)
	{
		ok=0;
		
		for (i=1;i<=m;++i)
		{
			if (d[y[i]]>d[x[i]]+c[i])
				d[y[i]]=d[x[i]]+c[i],
				ok=1;
			if (d[x[i]]>d[y[i]]-c[i])
				d[x[i]]=d[y[i]]-c[i],
				ok=1;
		}
	}
	
	printf("%d\n", d[w]);
}

int main()
{
	citire();
	solve();
	
	fclose(stdin);
	fclose(stdout);
	
	return 0;
	
}