#include <bits/stdc++.h>

using namespace std;

bool okay (unsigned short int i, unsigned short int j);

int N, M, X, Y, x, y, D;

vector <int> v[30001];
deque <int> q;
bool seen[30001];
int node;
int i;
int u[30001];

int sol[30001];

int main ()
{
    ifstream fin ("sate.in");
    fin >> N >> M >> X >> Y;
    for (i=1; i<=M; i++)
    {
        fin >> x >> y >> D;
        v[x].push_back(y);
        v[y].push_back(x);
        u[y] = D;
        u[x] = D;
    }
    fin.close();
    q.push_back(Y);
    seen[Y] = 1;
    sol[Y] = u[Y];
    while (!q.empty())
    {
        node = q.front();
        q.pop_front();
        for (i=0; i<v[node].size(); i++)
            if (seen[v[node][i]] == 0)
            {
                seen[v[node][i]] = 1;
                if (i > node)
                    sol[v[node][i]] = sol[node] - 1;
                else
                    sol[v[node][i]] = sol[node] + 1;
                q.push_back(v[node][i]);
            }
    }
    ofstream fout ("sate.out");
    fout << sol[X]-1;
    fout.close();
    return 0;
}

bool okay (unsigned short int i, unsigned short int j)
{
    if (i<1 || j<1 || i>N || j>N)
        return 0;
    return 1;
}