#include<bits/stdc++.h>

#define rep(i, n) for (int i = 0; i < (int) n; i++)

using ll = long long;
using namespace std;
using T = tuple<ll, ll, ll>;
using P = pair<ll, ll>;

const long long INF = 1ll << 60;

template<class T>
bool chmin(T &a, T b) {
    if (a > b) {
        a = b;
        return true;
    }
    return false;
}

template<class T>
bool chmax(T &a, T b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}


int main() {
    ll n, m, s, t;
    cin >> n >> m >> s >> t;
    s--;
    t--;
    vector<ll> p(n);
    rep(i, n) cin >> p[i];
    vector<vector<ll>> vertex(n);
    rep(i, m) {
        ll a, b;
        cin >> a >> b;
        a--;
        b--;
        vertex[a].push_back(b);
        vertex[b].push_back(a);
    }
    
    ll ans = 0;
    
    priority_queue<T> pri;
    vector<map<ll, ll>> seen(n);
    seen[s][0] = p[s];
    pri.emplace(p[s], s, 0);
    while (!pri.empty()) {
        auto[pi, i, score] = pri.top();
        pri.pop();
        if (i == t) chmax(ans, score);
        
        for (auto j : vertex[i]) {
            if (p[j] < pi) {
                pri.emplace(p[j], j, score + 1);
                seen[j][score + 1] = p[j];
            } else if (pi > seen[j][score]) {
                pri.emplace(pi, j, score);
                seen[j][score] = pi;
            }
        }
    }
    
    cout << ans << endl;
}