#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

struct Edge
{
	int f, s, t;
};

int main() {
	int n, m; cin >> n >> m;

	vector <Edge> v[n+1];
	bool visited[n+1]={false};
	ll distance[n+1];

	for (int i=1; i<=n; i++)
	distance[i]=pow(10,12);

	for (int i=1; i<=m; i++)
	{
		int x, y, z; cin >> x >> y >> z;
		v[x].push_back({y,z,i});
		v[y].push_back({x,z,i});
	}

	int x, y; ll c; cin >> x >> y >> c;
	distance[x]=0;

	int l=1, r=m, mid;

	while (l<r)
	{
		mid=(l+r)/2; //cout << l << " " << mid << " " << r << endl;

		priority_queue <pair<ll,int> > q; q.push({0,x});
		while (!q.empty())
		{
			int a=q.top().second; q.pop();
			if (visited[a])
			{
				//cout << "hi" << endl;
				continue;
			}
			visited[a]=true;

			for (int u=0; u<v[a].size(); u++)
			{
				int b=v[a][u].f, w=v[a][u].s;

				//cout << a << " " << b << "  " << v[a][u].t << " " << mid << endl << endl;

				if (v[a][u].t>mid) continue;

				if (distance[a]+w<distance[b])
				{
					distance[b]=distance[a]+w;
					q.push({-distance[b],b});
				}
			}
		}

		if (distance[y]<=c)
		{
			r=mid;

			for (int i=1; i<=n; i++)
			{
				distance[i]=pow(10,12);
				visited[i]=false;
			}
			distance[x]=0;
		}

		else if (distance[y]>c)
		{
			l=mid+1;

			//cout << l << " " << mid << " " << r << endl;

			if (l==m)
			{
				r++;
			}

			if (mid==m)
			{
				cout << -1;
				return 0;
			}

			for (int i=1; i<=n; i++)
			{
				distance[i]=pow(10,12);
				visited[i]=false;
			}
			distance[x]=0;
		}
	}

	cout << r;
}