#include <bits/stdc++.h>
using namespace std;
#define F first
#define S second
#define R cin>>
#define ll long long
#define ln cout<<'\n'
#define in(a) insert(a)
#define pb(a) push_back(a)
#define pd(a) printf("%.10f\n",a)
#define mem(a) memset(a,0,sizeof(a))
#define all(c) (c).begin(),(c).end()
#define iter(c) __typeof((c).begin())
#define rrep(i,n) for(ll i=(ll)(n)-1;i>=0;i--)
#define REP(i,m,n) for(ll i=(ll)(m);i<(ll)(n);i++)
#define rep(i,n) REP(i,0,n)
#define tr(it,c) for(iter(c) it=(c).begin();it!=(c).end();it++)
ll check(ll n,ll m,ll x,ll y){return x>=0&&x<n&&y>=0&&y<m;}void pr(){ln;}
template<class A,class...B>void pr(const A &a,const B&...b){cout<<a<<(sizeof...(b)?" ":"");pr(b...);}
template<class A>void PR(A a,ll n){rep(i,n)cout<<(i?" ":"")<<a[i];ln;}
const ll MAX=1e9+7,MAXL=1LL<<61,dx[8]={-1,0,1,0,-1,-1,1,1},dy[8]={0,1,0,-1,-1,1,1,-1};
typedef pair<ll,ll> P;

void Main() {
  ll n,m,s,t;
  cin >> n >> m >> s >> t;
  s--,t--;
  ll a[n];
  rep(i,n) R a[i];
  vector<ll> v[n];
  rep(i,m) {
    ll x,y;
    cin >> x >> y;
    x--,y--;
    v[x].pb(y);
    v[y].pb(x);
  }
  priority_queue<P> que;
  ll d[n];
  mem(d);
  d[s]=1;
  que.push(P(a[s],s));
  ll ans=0,q=a[s];
  while(!que.empty()) {
    P p=que.top();que.pop();
    ll x=p.S,c=p.F;
    if(c<q) {
      ans++;
      q=c;
    }
    rep(i,v[x].size()) {
      ll y=v[x][i];
      if(!d[y]) {
        d[y]=1;
        que.push(P(a[y],y));
      }
    }
  }
  pr(ans);
}

int main(){ios::sync_with_stdio(0);cin.tie(0);Main();return 0;}