local bls, brs = bit.lshift, bit.rshift
local Heapq = {}
Heapq.create = function(self, lt)
  self.lt = lt
  self.cnt = 0
  self.t = {}
end

Heapq.push = function(self, v)
  local hqlt = self.lt
  local hqt = self.t
  local c = self.cnt + 1
  self.cnt = c
  hqt[c] = v
  while 1 < c do
    local p = brs(c, 1)
    if hqlt(hqt[c], hqt[p]) then
      hqt[c], hqt[p] = hqt[p], hqt[c]
      c = p
    else
      break
    end
  end
end
Heapq.empty = function(self)
  return self.cnt == 0
end
Heapq.pop = function(self)
  local hqlt = self.lt
  local hqt = self.t
  local ret = hqt[1]
  local c = self.cnt
  hqt[1] = hqt[c]
  c = c - 1
  self.cnt = c
  local p = 1
  while true do
    local d1, d2 = p * 2, p * 2 + 1
    if c < d1 then break
    elseif c < d2 then
      if hqlt(hqt[d1], hqt[p]) then
        hqt[d1], hqt[p] = hqt[p], hqt[d1]
      end
      break
    else
      if hqlt(hqt[d1], hqt[d2]) then
        if hqlt(hqt[d1], hqt[p]) then
          hqt[d1], hqt[p] = hqt[p], hqt[d1]
          p = d1
        else break
        end
      else
        if hqlt(hqt[d2], hqt[p]) then
          hqt[d2], hqt[p] = hqt[p], hqt[d2]
          p = d2
        else break
        end
      end
    end
  end
  return ret
end

Heapq.new = function(lt)
  local obj = {}
  setmetatable(obj, {__index = Heapq})
  obj:create(lt)
  return obj
end

local n, m = io.read("*n", "*n")
local spos, tpos = io.read("*n", "*n")
local p = {}
local edge = {}
local asked = {}
for i = 1, n do
  p[i] = io.read("*n")
  edge[i] = {}
  asked[i] = false
end
for i = 1, m do
  local a, b = io.read("*n", "*n")
  table.insert(edge[a], b)
  table.insert(edge[b], a)
end
local function hqlt(a, b)
  return p[a] > p[b]
end
local hq = Heapq.new(hqlt)
asked[spos] = true
hq:push(spos)

local ret = 0
local curval = p[spos]
while not hq:empty() do
  local v = hq:pop()
  if p[v] < curval then
    ret = ret + 1
    curval = p[v]
  end
  for i = 1, #edge[v] do
    local dst = edge[v][i]
    if not asked[dst] then
      asked[dst] = true
      hq:push(dst)
    end
  end
end
print(ret)