#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
#define FOR(i,m,n) for(int i=(m);i<(n);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()
using ll = long long;
constexpr int INF = 0x3f3f3f3f;
constexpr long long LINF = 0x3f3f3f3f3f3f3f3fLL;
constexpr double EPS = 1e-8;
constexpr int MOD = 1000000007;
// constexpr int MOD = 998244353;
constexpr int dy[] = {1, 0, -1, 0}, dx[] = {0, -1, 0, 1};
constexpr int dy8[] = {1, 1, 0, -1, -1, -1, 0, 1}, dx8[] = {0, -1, -1, -1, 0, 1, 1, 1};
template <typename T, typename U> inline bool chmax(T &a, U b) { return a < b ? (a = b, true) : false; }
template <typename T, typename U> inline bool chmin(T &a, U b) { return a > b ? (a = b, true) : false; }
struct IOSetup {
  IOSetup() {
    std::cin.tie(nullptr);
    std::ios_base::sync_with_stdio(false);
    std::cout << fixed << setprecision(20);
  }
} iosetup;

int main() {
  int n, m, s, t; cin >> n >> m >> s >> t; --s; --t;
  vector<int> p(n); REP(i, n) cin >> p[i];
  vector<int> ps = p;
  sort(ALL(ps));
  ps.erase(unique(ALL(ps)), ps.end());
  REP(i, n) p[i] = lower_bound(ALL(ps), p[i]) - ps.begin();
  vector<vector<int>> graph(n);
  while (m--) {
    int a, b; cin >> a >> b; --a; --b;
    graph[a].emplace_back(b);
    graph[b].emplace_back(a);
  }
  vector<int> y(n, -1);
  y[s] = 0;
  vector<bool> visited(n, false);
  visited[s] = true;
  priority_queue<pair<int, int>> que;
  que.emplace(p[s], s);
  for (int i = p[s]; i >= 0; --i) {
    while (!que.empty() && que.top().first >= i) {
      auto [_, v] = que.top(); que.pop();
      visited[v] = true;
      for (int e : graph[v]) {
        if (p[e] < i) {
          chmax(y[e], y[v] + 1);
        } else {
          chmax(y[e], y[v]);
        }
        if (!visited[e]) que.emplace(p[e], e);
      }
    }
  }
  cout << *max_element(ALL(y)) << '\n';
  return 0;
}