#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <queue>
#include <string>
#include <map>
#include <set>
#include <stack>
#include <tuple>
#include <deque>
#include <array>
#include <numeric>
#include <bitset>
#include <iomanip>
#include <cassert>
#include <chrono>
#include <random>
#include <limits>
#include <iterator>
#include <functional>
#include <sstream>
#include <fstream>
#include <complex>
#include <cstring>
#include <unordered_map>
#include <unordered_set>
using namespace std;

using ll = long long;
constexpr int INF = 1001001001;
constexpr int mod = 1000000007;
// constexpr int mod = 998244353;

template<class T>
inline bool chmax(T& x, T y){
    if(x < y){
        x = y;
        return true;
    }
    return false;
}
template<class T>
inline bool chmin(T& x, T y){
    if(x > y){
        x = y;
        return true;
    }
    return false;
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    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].emplace_back(b);
        g[b].emplace_back(a);
    }

    vector<int> dist(n, INF);
    dist[s] = 0;
    int X = p[s], Y = 0;
    using node = pair<int, int>;
    priority_queue<node> que;
    que.emplace(p[s], s);
    while(!que.empty()){
        auto [val, from] = que.top();
        que.pop();
        if(X > val) X = val, Y += 1;
        for(int to : g[from]){
            if(chmin(dist[to], dist[from] + 1)){
                que.emplace(p[to], to);
            }
        }
    }

    cout << Y << endl;

    return 0;
}