#include <fstream>
#include <vector>
#include <queue>
using namespace std;
ifstream f("sate.in");
ofstream g("sate.out");
int n,m,x,y,x1,y1,i,z,j,c,d[30001];
vector <pair<int,int> > v[30001];
queue <int> q;
int main()
{
    f>>n>>m>>x>>y;
    for (i=1;i<=n;i++)
        d[i]=1<<31-1;
    for (i=1;i<=m;i++)
    {
    f>>x1>>y1>>c;
    v[x1].push_back(make_pair(y1,c));
    v[y1].push_back(make_pair(x1,-c));
    }
    q.push(x);
    d[x]=0;
    while(!q.empty())
    {
        z=q.front();
        q.pop();
        for (j=0;j<v[z].size();j++)
            if (d[v[z][j].first]>d[z]+v[z][j].second)
            d[v[z][j].first]=d[z]+v[z][j].second,q.push(v[z][j].first);
    }
    g<<d[y]<<' ';
    return 0;
}