#include <fstream>
#include <vector>
using namespace std;
ifstream f("sate.in");
ofstream g("sate.out");
int n,m,x,y,x1,y1,d,used[30001];
vector <int> graf[30001],dist[30001];
int dfs(int k)
{
    used[k]=1;
    int len=graf[k].size();
    for(int it=0;it<len;it++)
    {
        if(!used[graf[k][it]])
        {
            if(graf[k][it]==y)
                for(int i=1;i<=n;i++)
                    used[i]=1;
            if(k<graf[k][it])
                return dist[k][it]+dfs(graf[k][it]);
            else
                return (-dist[k][it])+dfs(graf[k][it]);
        }
    }
}
int main()
{
    f>>n>>m>>x>>y;
    for(int i=1;i<=m;i++)
    {
        f>>x1>>y1>>d;
        graf[x1].push_back(y1);
        graf[y1].push_back(x1);
        dist[x1].push_back(d);
        dist[y1].push_back(d);
    }
    g<<dfs(x);
    return 0;
}