Baekjoon #20007

import java.util.*;
import java.io.*;

public class Main {
    public static void main(String[] args) {
        FastReader rd = new FastReader();
        int N = rd.nextInt();
        int M = rd.nextInt();
        int X = rd.nextInt();
        int Y = rd.nextInt();


        int INF = (int) 1e7 + 4;
        int[] dist = new int[N];
        Arrays.fill(dist, INF);


        List<int[]> list[] = new ArrayList[N];
        for (int i = 0; i < N; i++) {
            list[i] = new ArrayList<>();
        }

        for (int i = 0; i < M; i++) {
            int n1 = rd.nextInt();
            int n2 = rd.nextInt();
            int d = rd.nextInt();
            list[n1].add(new int[]{n2, d});
            list[n2].add(new int[]{n1, d});
        }

        PriorityQueue<int[]> pq = new PriorityQueue<>((n1, n2) -> n1[1] - n2[1]);
        pq.add(new int[]{Y, 0});
        dist[Y] = 0;

        while (!pq.isEmpty()) {
            int[] curr = pq.poll();

            for (int[] next : list[curr[0]]) {
                if (dist[next[0]] > curr[1] + next[1]) {
                    dist[next[0]] = curr[1] + next[1];
                    pq.add(new int[]{next[0], dist[next[0]]});
                }
            }
        }

        Arrays.sort(dist);
        int sum = 0;
        int ans = 1;
        for (int i = 0; i < dist.length; i++) {
            if (dist[i] * 2 > X) {
                ans = -1;
                break;
            }

            sum += dist[i] * 2;
            if (sum > X) {
                sum = dist[i] * 2;
                ans++;
            }
        }

        System.out.println(ans);
    }

    static class FastReader {
        BufferedReader br;
        StringTokenizer st;

        public FastReader() {
            br = new BufferedReader(new InputStreamReader(System.in));
        }

        String next() {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

        int nextInt() {
            return Integer.parseInt(next());
        }

        long nextLong() {
            return Long.parseLong(next());
        }

        double nextDouble() {
            return Double.parseDouble(next());
        }

        String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }
    }
}