#include<iostream>
#include <fstream>
#include<vector>
#include<string>
using namespace std;
vector<short> v[30001];
vector<int> c[30001];
short q[30001],p,u;
int n,m,x,y,a,b,i,fix,cost[30001],dist,s,num,ce;
string str;
int getnum()
{
    num=0;
    while(str[ce]>='0'&&str[ce]<='9')
        {num=num*10+str[ce]-'0';ce++;}
    ce++;
    return num;
}
int main()
{
    ifstream f("sate.in");
    ofstream g("sate.out");
    f>>n>>m>>x>>y;f.get();
    for(i=1;i<=m;i++)
    {
        ce=0;
        getline(f,str);
        a=getnum();
        b=getnum();
        dist=getnum();
        if(b<a) swap(a,b);
        v[a].push_back(b);
        v[b].push_back(a);
        c[b].push_back(dist);
        dist*=-1;
        c[a].push_back(dist);

    }

    cost[x]=0;
    p=1;
    u=1;
    q[p]=x;
    while(p<=u&&cost[y]==0)
    {
        s=q[p];
        p++;
        fix=v[s].size();
        for(i=0;i<fix;i++)
        {
            if(cost[v[s][i]]==0&&v[s][i]!=x)
            {cost[v[s][i]]=cost[s]+c[s][i];
            u++;q[u]=v[s][i];if(v[s][i]==y)break;}
        }
    }
    if(cost[y]<0) cost[y]*=-1;
    g<<cost[y];

    return 0;
}