#include <bits/stdc++.h>
using namespace std;

int main() {
    int N, M, S, T;
    cin >> N >> M >> S >> T;
    S--; T--;
    vector<int> p(N);
    for (int i = 0; i < N; i++) cin >> p[i];

    vector<vector<int>> G(N);
    for (int i = 0; i < M; i++) {
        int a, b;
        cin >> a >> b;
        a--; b--;
        G[a].push_back(b);
        G[b].push_back(a);
    }
    
    priority_queue<pair<int, int>> que;
    vector<bool> seen(N, false);
    seen[S] = true;

    for (auto nv : G[S]) que.emplace(p[nv], nv);
    int ans = 0;
    int mini = p[S];
    while (!que.empty()) {
        auto pa = que.top();
        que.pop();
        int v = pa.second;
        seen[v] = true;

        if (pa.first < mini) {
            mini = pa.first;
            ans++;
        }
        for (auto nv : G[v]) {
            if (seen[nv]) continue;
            que.emplace(p[nv], nv);
        }
    }

    cout << ans << endl;
}