#include <fstream>
#include <cstring>
#include <vector>
using namespace std;
ifstream f("sate.in");
ofstream g("sate.out");
vector < pair <int, int > > graf[30001];
int D, dis, x, y, Nods, Arcs, Origin, End, i;
bool ok, viz[30001];
void dfs(int node){
    viz[node] = 1;
    for(int i = 0; i < graf[node].size(); i++){
        if(ok == 1)
            return;
        if(viz[graf[node][i].first] == 0){
            D = D + graf[node][i].second;
            if(graf[node][i].first == End){
                g << D;
                ok = 1;
            }
            dfs(graf[node][i].first);
            D = D - graf[node][i].second;
        }
    }
}
int main()
{   f >> Nods >> Arcs >> Origin >> End;
    for(i = 1; i <= Arcs; i++){
        f >> x >> y >> dis;
        if(x > y)
            swap(x, y);
        graf[x].push_back({y, dis});
        graf[y].push_back({x, -dis});
    }
    dfs(Origin);
    return 0;
}