#include <bits/stdc++.h>

using namespace std;
typedef long long ll;
#define mp(a, b) make_pair(a, b)

int main()
{
    ll n, m, a, b, dp[100010], x, y, w, INF = 1e15, temp;
    queue <ll> q;
    cin >> n >> m;
    for (ll i = 0; i < n; i++)
        dp[i] = INF;
    vector <vector <pair <ll, ll> > > g(n);
    for (ll i = 0; i < m; i++){
        cin >> x >> y >> w;
        g[x - 1].push_back(mp(w, y - 1));
    }
    cin >> a >> b;
    for (ll z = 0; z < n; z++)
        sort(g[z].begin(), g[z].end());
    dp[a - 1] = 0;
    q.push(a - 1);
    while (!q.empty()){
        temp = q.front();
        q.pop();
        for (ll i = 0; i < g[temp].size(); i++)
            if (dp[g[temp][i].second] > max(dp[temp], max((ll)g[temp].size() - 1 - i - 1,(ll) 0))){
                dp[g[temp][i].second] = max(dp[temp], max((ll)g[temp].size() - 1 - i - 1,(ll) 0));
                q.push(g[temp][i].second);
            }
    }
    if (dp[b - 1] == INF)
        cout << -1;
    else
        cout << dp[b - 1];
    cout << endl;
    return 0;
}