class UnionFind:
    def __init__(self, n):
        self.par = [i for i in range(n+1)]
        self.rank = [0] * (n + 1)
        self.size = [1] * (n + 1)
 
    # 検索
    def find(self, x):
        if self.par[x] == x:
            return x
        else:
            self.par[x] = self.find(self.par[x])
            return self.par[x]
 
    # 併合
    def unite(self, x, y):
        x = self.find(x)
        y = self.find(y)
        if x == y:
            return
        if self.rank[x] < self.rank[y]:
            self.par[x] = y
            self.size[y] += self.size[x]
        else:
            self.par[y] = x
            self.size[x] += self.size[y]
            if self.rank[x] == self.rank[y]:
                self.rank[x] += 1
 
    # 同じ集合に属するか判定
    def same_check(self, x, y):
        return self.find(x) == self.find(y)

def compress(arr):
    return {e: i for i, e in enumerate(sorted(set(arr)))}

n, m, s, t = map(int, input().split())
p = list(map(int, input().split()))
c = compress(p)
for i in range(n):
    p[i] = c[p[i]]
edges = []
for _ in range(m):
    a, b = map(int, input().split())
    if p[a - 1] < p[b - 1]:
        edges.append((a - 1, b - 1))
    else:
        edges.append((b - 1, a - 1))
edges.sort(key=lambda x:p[x[0]], reverse=True)
uf = UnionFind(n)
idx = 0
ans = 0
while idx < m and p[edges[idx][0]] >= p[s - 1]:
    uf.unite(edges[idx][0], edges[idx][1])
    idx += 1
for x in range(p[s - 1] - 1, -1, -1):
    flg = 0
    while idx < m and p[edges[idx][0]] >= x:
        uf.unite(edges[idx][0], edges[idx][1])
        if uf.same_check(edges[idx][0], s - 1):
            flg = 1
        idx += 1
    if flg:
        ans += 1
print(ans)