#include<fstream>
#include<vector>
using namespace std;
vector < pair < int, int > > v[30005];
int viz[30005],n,m,a,b,x,y,c;
void dfs(int nod)
{
    for(int i=0;i<v[nod].size();++i){
        int fs=v[nod][i].first;
        int cost=v[nod][i].second;
        if(!viz[fs]){
            viz[fs]=viz[nod]+cost;
            dfs(fs);
        }
    }
}
int main()
{
    ifstream f("sate.in");
    ofstream g("sate.out");
    f>>n>>m>>a>>b;
    if(a>b)
        swap(a,b);
    for(int i=1;i<=m;++i)
    {
        f>>x>>y>>c;
        v[x].push_back(make_pair(y,c));
        v[y].push_back(make_pair(x,-c));
    }
    dfs(a);
    g<<viz[b];
    return 0;
}