#include<cstdio>
#include<cstring>
#define N 30001
typedef struct nod
{int info,cost;
struct nod *next;}Nod;
bool c[N];
Nod *l[N],*t;
char r[100];
int i,n,m,x,y,j,p,u,k,s[N],q,v[6],o,e;

void A(int i,int j,int k)
{Nod *p=new Nod;
p->info=j,p->cost=k,p->next=l[i],l[i]=p;}

int B(int i,int j)
{for(Nod *p=l[i];p;p=p->next)
if(p->info==j)
      return p->cost;
return 0;}

int main()
{FILE *f=fopen("sate.in","r"),*g=fopen("sate.out","w");
fgets(r,100,f);
q=strlen(r)-1;
for(i=0;i<q;i++)
if(r[i]>='0'&&r[i]<='9')
      v[o]=v[o]*10+(r[i]-'0');
else
      o++;
n=v[0],m=v[1],x=v[2],y=v[3],c[x]=1;
while(m--)
      {v[0]=v[1]=v[2]=0;
      fgets(r,100,f);
      q=strlen(r)-1,o=0;
      for(e=0;e<q;e++)
      if(r[e]>='0'&&r[e]<='9')
            v[o]=v[o]*10+(r[e]-'0');
      else
            o++;
      A(v[0],v[1],v[2]),A(v[1],v[0],-v[2]);}
for(t=l[x];t;t=t->next)
      s[u++]=t->info;
for(i=x;p<u;p++)
      {if(c[y])
             break;
      j=s[p],c[j]=1;
      for(t=l[j];t;t=t->next)
             {k=t->info;
             if(!c[k])       
                    {s[u++]=k;
                    if(i<j)
                           if(k<i)
                                  A(k,i,B(k,j)-B(i,j));
                           else
                                  A(i,k,B(j,k)+B(i,j));
                    else
                           if(k<i)
                                  A(k,i,B(j,i)+B(k,j));
                           else
                                  A(i,k,B(j,k)-B(j,i));}}}
fprintf(g,"%d",B(x,y));
return 0;}