#include<stdio.h>
#include<stdbool.h>
#include<limits.h>
int
a[40000],b[40000],c[40000],q[20000],d[20000],f[20000];
bool
vis[20000]={false};
int
x,y,z,sum,n,m,i,s,t;

void
qsort(int head, int tail)
{
    int
    i,j,x,y,z;
    i=head;j=tail;
    x=a[head];y=b[head];z=c[head];
    while(i<j)
    {
        while((i<j)&&(a[j]>=x)) j--;
        a[i]=a[j];b[i]=b[j];c[i]=c[j];
        while((i<j)&&(a[i]<=x)) i++;
        a[j]=a[i];b[j]=b[i];c[j]=c[i];
    }
    a[i]=x;b[i]=y;c[i]=z;
    if (head<(i-1)) qsort(head,i-1);
    if ((i+1)<tail) qsort(i+1,tail);
}

void
spfa(int s)
{
  int
  i,k,head,tail;
  for (i=1;i<=n;i++)
  d[i]=INT_MAX >> 1;
  d[s]=0;
  head=0;tail=1;
  q[1]=s;
  vis[s]=true;
  
  while (head<tail)
  {
    head=head%10000+1;
    k=q[head];
    for (i=f[k];i<=(f[k+1]-1);i++)
    if ((d[k]+c[i])<d[b[i]])
    {
        d[b[i]]=d[k]+c[i];
        if (vis[b[i]]==false)
        {
            tail=tail%10000+1;
            q[tail]=b[i];
            vis[b[i]]=true;
        }
    }
    vis[k]=false;
  }
}

int
main(void)
{
    scanf("%d%d%d%d\n",&n,&m,&s,&t);
    sum=0;
    for(i=1;i<=m;i++)
    {
        scanf("%d%d%d",&x,&y,&z);
        sum++;
        a[sum]=x;
        b[sum]=y;
        c[sum]=z;
        sum++;
        b[sum]=x;
        a[sum]=y;
        c[sum]=z;
    }
    m=m*2;
    qsort(1,m);
    for(i=1;i<=m;i++)
    if (f[a[i]]==0) f[a[i]]=i;
    f[n+1]=m+1;
    for (i=n;i>=1;i--)
    if (f[i]==0) f[i]=f[i+1];
    spfa(s);
    printf("%d\n",d[t]);
    return 0;
}