#include <fstream>
#include <vector>
using namespace std;
ifstream f("sate.in"); ofstream g("sate.out");
const int Nmax=30001;
vector < pair<int, int> > v[30001];
int n, m, cost[Nmax];
void dfs(int x)
{    for(unsigned int i=0;i<v[x].size();i++)
        if(cost[x]+v[x][i].second<cost[v[x][i].first])
        {
            cost[v[x][i].first]=cost[x]+v[x][i].second;
            dfs(v[x][i].first);
        }
}
int main()
{   int a,b,x,y,c;
    f>>n>>m>>a>>b;
    for(int i=1; i<=n; i++) cost[i]=999999999;
    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));
    }
    cost[a] = 0;
    dfs(a);
    g<<cost[b]<<'\n';
    return 0;
}