#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < int(n); i++)
#define rrep(i,n) for(int i = int(n)-1; i >= 0; i--)
#define all(a) a.begin(),a.end()
#define rall(a) a.rbegin(),a.rend()
#define pb push_back
using namespace std;
using ll = long long;
using P = pair<ll,ll>;
template<class T> bool chmax(T &a, const T &b) {if(a < b) {a = b; return true;} return false;}
template<class T> bool chmin(T &a, const T &b) {if(b < a) {a = b; return true;} return false;}
int dx[] = {1, 0,-1, 0, 1, 1,-1,-1};
int dy[] = {0, 1, 0,-1, 1,-1, 1,-1};
ll mod = 998244353;
ll MOD = 1000000007;
ll inf = 1001001001;
ll INF = 1001001001001001001;
struct UnionFind {
    vector<int>par;
    vector<int>size;
    UnionFind(int x) {
        par.resize(x);
        size.resize(x, 1);
        for(int i = 0; i < x; i++) {
            par[i] = i;
        }
    }
    int find(int x) {
        if(par[x] == x) {
            return x;
        }
        return par[x] = find(par[x]);
    }
    bool same(int x, int y) {
        return find(x) == find(y);
    }
    int consize(int x) {
        return size[find(x)];
    }
    void unite(int x, int y) {
        x = find(x);
        y = find(y);
        if(x == y) {
            return;
        }
        if(size[x] < size[y]) {
            par[x] = y;
            size[y] += size[x];
        }
        else {
            par[y] = x;
            size[x] += size[y];
        }
    }
};
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<vector<int>>road(N);
    rep(i,M) {
        int a,b;
        cin >> a >> b;
        a--;b--;
        road[a].pb(b);
        road[b].pb(a);
    }
    queue<int>que;
    que.push(S);
    UnionFind uf(N);
    int res = p[S];
    int ans = 0;
    set<pair<int,int>>st;
    while(true) {
        while (!que.empty()) {
            int x = que.front();
            que.pop();
            rep(i,road[x].size()) {
                if(p[road[x][i]] >= res) {
                    if(!uf.same(x,road[x][i])) {
                        uf.unite(x,road[x][i]);
                        que.push(road[x][i]);
                    }
                }
                else {
                    if(!uf.same(x,road[x][i])) {
                        uf.unite(x,road[x][i]);
                        st.insert({p[road[x][i]],road[x][i]});
                    }
                }
            }
        }
        if(st.size() == 0) {
            break;
        }
        else {
            ans++;
            pair<int,int> x = *st.rbegin();
            auto it = st.end();
            it--;
            while(true) {
                if(it->first != x.first) {
                    break;
                }
                que.push(it->second);
                if(it == st.begin()){
                    st.erase(it);
                    break;
                }
                st.erase(it--);
            }
            chmin(res,x.first);
        }
    }
    cout << ans << endl;
}