#include <fstream>
#include <vector>
#include <queue>
using namespace std;

ifstream is("sate.in");
ofstream os("sate.out");

int n, m, x, y;
vector<vector<pair<int, int> > > c;
vector<bool> ok;
queue<pair<int, int> > q;

void READ();

int main()
{
    READ();
    q.push(make_pair(x, 0));
    int w, d;
    pair<int, int> nod;
    while ( !q.empty() )
    {
        w = q.front().first;
        d = q.front().second;
        q.pop();
        if ( w == y )
        {
            os << d;
            break;
        }
        for ( vector<pair<int, int> >::iterator it = c[w].begin(); it != c[w].end(); ++it )
        {
            nod = *it;
            if ( ok[nod.first] )
                continue;
            ok[nod.first] = true;
            if ( w > nod.first )
                q.push(make_pair(nod.first, d - nod.second));
            else
                q.push(make_pair(nod.first, d + nod.second));
        }
    }
    is.close();
    os.close();
    return 0;
}

void READ()
{
    is >> n >> m >> x >> y;
    int i, j, d;
    c.resize(n + 1);
    ok.resize(n + 1);
    while ( m-- )
    {
        is >> i >> j >> d;
        c[i].push_back(make_pair(j, d));
        c[j].push_back(make_pair(i, d));
    }
}