#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;
int dp[100005];
int main() {
    int N,M,S,T;
    cin >> N >> M >> S >> T;
    vector<P>p(N);
    int mx = 0;
    rep(i,N) {
        cin >> p[i].first;
        p[i].second = i;
        if(i+1 == S) {
            mx = (int)p[i].first;
        }
    }
    vector<vector<P>>road(N);
    rep(i,M) {
        int a,b;
        cin >> a >> b;
        a--;b--;
        if(p[a].first > p[b].first) {
            road[a].pb({b,1});
            road[b].pb({a,0});
        }
        else if(p[a].first < p[b].first){
            road[b].pb({a,1});
            road[a].pb({b,0});
        }
        else {
            road[a].pb({b,0});
            road[b].pb({a,0});
        }
    }
    rep(i,N) {
        if(p[i].first > mx) {
            p[i].first = -1;
        }
    }
    S--;T--;
    sort(rall(p));
    map<int,int>key;
    int k = 1000000;
    rep(i,N) {
        key[(int)p[i].second] = i;
        if(p[i].first == mx) {
            chmin(k,i);
        }
    }
    for(int i = 0; i < N; i++) {
        rep(j,road[p[i].second].size()) {
            chmax(dp[key[(int)road[p[i].second][j].first]],(int)(dp[i]+road[p[i].second][j].second));
        }
    }
    cout << dp[key[(int)T]] << endl;
}