#include<stdio.h>
struct orase
  {
    int o,d;
    } *a[30002];
int nr[30002],c[2][30002],u,p,d,x,y,i,j,z,n,m,viz[30002];

int main(){
	FILE *f,*g; f=fopen("sate.in","r");
	g=fopen("sate.out","w");

fscanf(f,"%d %d %d %d",&n,&m,&x,&y);
for(i=1;i<=m;i++){
    fscanf(f,"%d %d %d",&x,&y,&d);
	nr[x]++;
     nr[y]++;
     }
fclose(f);
FILE * s=fopen("sate.in","r");
fscanf(s,"%d %d %d %d",&n,&m,&x,&y);
  for(i=0;i<=n;i++)
   {  a[i]=new orase[nr[i]+1];
    a[i][0].d=0;
    }
for(i=1;i<=m;i++){
	fscanf(s,"%d %d %d",&z,&j,&d);
    a[z][0].d++;
    a[z][a[z][0].d].o=j;
    a[z][a[z][0].d].d=d;
    a[j][0].d++;
    a[j][a[j][0].d].o=z;
    a[j][a[j][0].d].d=d;
    }
fclose(s);

u=1;p=1;  c[0][p]=x; viz[x]=1;

	for(i=1;i<=a[x][0].d;i++)
		{u++;
		 c[0][u]=a[x][i].o;
		 viz[c[0][u]]=1;
		 c[1][u]=a[x][i].d;
		 if (c[0][u]==y){
			 j=u;
			 u=0;
		   break;
		 }
	    }

p++;
while(p<=u){  
	   for(i=1;i<=a[c[0][p]][0].d;i++)
		   if(viz[a[c[0][p]][i].o]==0){
			   
			   viz[a[c[0][p]][i].o]=1;			   
			   if(a[c[0][p]][i].o<x&&c[0][p]<a[c[0][p]][i].o)
			   { u++; c[0][u]=a[c[0][p]][i].o;
			          c[1][u]=c[1][p]-a[c[0][p]][i].d;
			   }
			   else if(c[0][p]<x&&a[c[0][p]][i].o>x)
			   { u++; c[0][u]=a[c[0][p]][i].o;
					   c[1][u]=a[c[0][p]][i].d-c[1][p];
			   }
			   else if(x<c[0][p]&&c[0][p]<a[c[0][p]][i].o)
			   { u++; c[0][u]=a[c[0][p]][i].o;
					c[1][u]=c[1][p]+a[c[0][p]][i].d;}
			   else if(a[c[0][p]][i].o<c[0][p]&&c[0][p]<x)
			   { u++; c[0][u]=a[c[0][p]][i].o;
					  c[1][u]=c[1][p]+a[c[0][p]][i].d;}
			   else if(a[c[0][p]][i].o>x&&c[0][p]>a[c[0][p]][i].o)
			   { u++; c[0][u]=a[c[0][p]][i].o;
			                c[1][u]=c[1][p]-a[c[0][p]][i].d;
			   }
		   
			   if(c[0][u]==y){
			    p=u;
		        break;
		   }	
		   }
	
    	p++;
}
if(u==0)u=j;
fprintf(g,"%d",c[1][u]);
fclose(g);
return 0;
}