#include <bits/stdc++.h>
using namespace std;
using uint = unsigned int;
using ll = long long;
using ull = unsigned long long;
using pii = pair<int, int>;
using pll = pair<long long, long long>;
template <class T> using vec = vector<T>;
template <class T> using vvec = vector<vector<T>>;
#define rep(i, n) for (int i = 0; i < (n); i++)
#define rrep(i, n) for (int i = int(n) - 1; i >= 0; i--)
#define all(x) begin(x), end(x)
constexpr char ln = '\n';
template <class Container> inline int SZ(const Container& v) { return int(v.size()); }
template <class T> inline void UNIQUE(vector<T>& v) { v.erase(unique(v.begin(), v.end()), v.end()); }
template <class T1, class T2> inline bool chmax(T1& a, T2 b) { if (a < b) { a = b; return true; } return false; }
template <class T1, class T2> inline bool chmin(T1& a, T2 b) { if (a > b) { a = b; return true; } return false; }
inline int topbit(ull x) { return x == 0 ? -1 : 63 - __builtin_clzll(x); }
inline int botbit(ull x) { return x == 0 ? 64 : __builtin_ctzll(x); }
inline int popcount(ull x) { return __builtin_popcountll(x); }
inline int kthbit(ull x, int k) { return (x >> k) & 1; }
inline constexpr long long TEN(int x) { return x == 0 ? 1 : TEN(x - 1) * 10; }
const string YESNO[2] = {"NO", "YES"};
const string YesNo[2] = {"No", "Yes"};
inline void YES(bool t = true) { cout << YESNO[t] << "\n"; }
inline void Yes(bool t = true) { cout << YesNo[t] << "\n"; }
template <class T> inline void drop(T x) { cout << x << "\n"; exit(0); }
inline void print() { cout << "\n"; }
template <class T> inline void print(const vector<T>& v) { for (auto it = v.begin(); it != v.end(); ++it) { if (it != v.begin()) { cout << " "; } cout << *it; } print(); }
template <class T, class... Args> inline void print(const T& x, const Args& ... args) { cout << x << " "; print(args...); }
#ifdef MINATO_LOCAL
template <class T1, class T2> ostream& operator<<(ostream& os, pair<T1, T2> p) { return os << "(" << p.first << ", " << p.second << ")"; }
template <size_t N, class TUPLE> void debug_tuple(ostream& os, TUPLE _) { (void)os; (void)_; }
template <size_t N, class TUPLE, class T, class ...Args> void debug_tuple(ostream &os, TUPLE t) { os << (N == 0 ? "" : ", ") << get<N>(t); debug_tuple<N + 1, TUPLE, Args...>(os, t); }
template <class ...Args> ostream& operator<<(ostream& os, tuple<Args...> t) { os << "("; debug_tuple<0, tuple<Args...>, Args...>(os, t); return os << ")"; }
string debug_delim(int& i) { return i++ == 0 ? "" : ", "; }
#define debug_embrace(x) { int i = 0; os << "{";  { x } return os << "}"; }
template <class T> ostream& operator<<(ostream& os, vector<T> v) { debug_embrace( for (T e : v) { os << debug_delim(i) << e; } ) }
template <class T, size_t N> ostream& operator<<(ostream& os, array<T, N> a) { debug_embrace( for (T e : a) { os << debug_delim(i) << e; } ) }
template <class T, size_t N> enable_if_t<!is_same_v<char, remove_cv_t<T>>, ostream>& operator<<(ostream& os, T(&a)[N]) { debug_embrace( for (T e : a) { os << debug_delim(i) << e; } ) }
template <class Key> ostream& operator<<(ostream& os, set<Key> s) { debug_embrace( for (Key e : s) { os << debug_delim(i) << e; }) }
template <class Key, class T> ostream& operator<<(ostream& os, map<Key, T> mp) { debug_embrace( for (auto e : mp) { os << debug_delim(i) << e; }) }
template <class Key> ostream& operator<<(ostream& os, multiset<Key> s) { debug_embrace( for (Key e : s) { os << debug_delim(i) << e; }) }
template <class T> ostream& operator<<(ostream& os, queue<T> q) { debug_embrace( for (; !q.empty(); q.pop()) { os << debug_delim(i) << q.front(); } ) }
template <class T> ostream& operator<<(ostream& os, deque<T> q) { debug_embrace( for (T e : q) { os << debug_delim(i) << e; } ) }
template <class T> ostream& operator<<(ostream& os, priority_queue<T> q) { debug_embrace( for (; !q.empty(); q.pop()) { os << debug_delim(i) << q.top(); } ) }
template <class T> ostream& operator<<(ostream& os, priority_queue<T, vector<T>, greater<T>> q) { debug_embrace( for (; !q.empty(); q.pop()) { os << debug_delim(i) << q.top(); } ) }
void debug_out() { cerr << endl; }
template <class T, class... Args> void debug_out(const T& x, const Args& ... args) { cerr << " " << x; debug_out(args...); }
#define debug(...) cerr << __LINE__ << " : [" << #__VA_ARGS__ << "] =", debug_out(__VA_ARGS__)
#else
#define debug(...) (void(0))
#endif
struct fast_ios { fast_ios() { cin.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(20); cerr << fixed << setprecision(7); }; } fast_ios_;
///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

struct UnionFind {
  public:
    UnionFind() : n_(0) {}
    UnionFind(int n) : n_(n), group_num(n), node(n, -1) {}

    int size() const { return n_; }

    int count() const { return group_num; }

    bool merge(int x, int y) {
        assert(0 <= x and x < n_);
        assert(0 <= y and y < n_);
        x = root_(x); y = root_(y);
        if (x == y) return false;
        if (node[x] > node[y]) swap(x,y);
        node[x] += node[y];
        node[y] = x;
        group_num--;
        return true; 
    }

    template <class F>
    bool merge(int x, int y, const F& f) {
        assert(0 <= x and x < n_);
        assert(0 <= y and y < n_);
        x = root_(x); y = root_(y);
        if (x == y) return false;
        if (node[x] > node[y]) swap(x,y);
        node[x] += node[y];
        node[y] = x;
        group_num--;
        f(x, y);
        return true;
    }

    bool same(int x, int y) {
        assert(0 <= x and x < n_);
        assert(0 <= y and y < n_);
        return root_(x) == root_(y); 
    }

    int root(int x) {
        assert(0 <= x and x < n_);
        return root_(x);
    }

    int size(int x) { 
        assert(0 <= x and x < n_);
        return -node[root_(x)]; 
    }

    int operator[](int x) {
        assert(0 <= x and x < n_);
        return root_(x);
    }

    vector<vector<int>> groups() {
        vector<int> leader_buf(n_), group_size(n_);
        for (int i = 0; i < n_; i++) {
            leader_buf[i] = root(i);
            group_size[leader_buf[i]]++;
        }
        vector<vector<int>> result(n_);
        for (int i = 0; i < n_; i++) {
            result[i].reserve(group_size[i]);
        }
        for (int i = 0; i < n_; i++) {
            result[leader_buf[i]].push_back(i);
        }
        result.erase(
            remove_if(result.begin(), result.end(),
                      [&](const vector<int>& v) { return v.empty(); }),
            result.end());
        return result;
    }

  private:
    int n_, group_num;
    vector<int> node;

    int root_(int x) {
        if (node[x] < 0) return x;
        return node[x] = root_(node[x]);
    }
};

int main() {
    int N,M,S,T; cin >> N >> M >> S >> T;
    S--; T--;
    vec<int> P(N);
    rep(i,N) cin >> P[i];
    vvec<int> G(N);
    rep(i,M) {
        int u,v; cin >> u >> v;
        u--; v--;
        G[u].emplace_back(v);
        G[v].emplace_back(u);
    }

    map<int, vec<int>, greater<int>> dic;
    rep(i,N) {
        dic[P[i]].emplace_back(i);
    } 

    UnionFind uf(N);
    const int INF = 1e9;
    vec<int> dp(N,-INF);
    dp[S] = 0;
    for (auto& [key,arr] : dic) {
        for (int u : arr) {
            for (int v : G[u]) {
                if (P[v] <= P[u]) continue;
                if (dp[uf[v]]==-INF) continue;
                chmax(dp[u],dp[uf[v]]+1);
            }
        }
        for (int u : arr) {
            for (int v : G[u]) {
                if (P[v] >= P[u]) {
                    uf.merge(u, v, [&](int x, int y){
                        chmax(dp[x],dp[y]);
                    });
                }
            }
        }
    }

    cout << *max_element(all(dp)) << ln;
}