package main

import (
	"bufio"
	"fmt"
	"math"
	"os"
	"sort"
	"strconv"
)

var sc = bufio.NewScanner(os.Stdin)
var wr = bufio.NewWriter(os.Stdout)

func out(x ...interface{}) {
	fmt.Fprintln(wr, x...)
}

func getI() int {
	sc.Scan()
	i, e := strconv.Atoi(sc.Text())
	if e != nil {
		panic(e)
	}
	return i
}

func getF() float64 {
	sc.Scan()
	i, e := strconv.ParseFloat(sc.Text(), 64)
	if e != nil {
		panic(e)
	}
	return i
}

func getInts(N int) []int {
	ret := make([]int, N)
	for i := 0; i < N; i++ {
		ret[i] = getI()
	}
	return ret
}

func getS() string {
	sc.Scan()
	return sc.Text()
}

// min, max, asub, absなど基本関数
func max(a, b int) int {
	if a > b {
		return a
	}
	return b
}

func min(a, b int) int {
	if a < b {
		return a
	}
	return b
}

// min for n entry
func nmin(a ...int) int {
	ret := a[0]
	for _, e := range a {
		ret = min(ret, e)
	}
	return ret
}

// max for n entry
func nmax(a ...int) int {
	ret := a[0]
	for _, e := range a {
		ret = max(ret, e)
	}
	return ret
}

func asub(a, b int) int {
	if a > b {
		return a - b
	}
	return b - a
}

func abs(a int) int {
	if a >= 0 {
		return a
	}
	return -a
}

func lowerBound(a []int, x int) int {
	idx := sort.Search(len(a), func(i int) bool {
		return a[i] >= x
	})
	return idx
}

func upperBound(a []int, x int) int {
	idx := sort.Search(len(a), func(i int) bool {
		return a[i] > x
	})
	return idx
}

var N, M, S, T int
var p []int
var node [][]int
var used []bool
var dist []int
var xx []int

func dfs(v, x, y, flg int) {
	if used[v] {
		return
	}
	if flg == 0 {
		if x > p[v] {
			x = p[v]
			y++
		}
		xx[v] = x
		dist[v] = y
		used[v] = true
	}
	for _, e := range node[v] {
		if e == v {
			continue
		}
		dfs(e, x, y, 0)
	}
}

func main() {
	defer wr.Flush()
	sc.Split(bufio.ScanWords)
	sc.Buffer([]byte{}, math.MaxInt32)
	// this template is new version.
	// use getI(), getS(), getInts(), getF()
	N, M, S, T = getI(), getI(), getI()-1, getI()-1
	p = getInts(N)
	node = make([][]int, N)
	for i := 0; i < M; i++ {
		a, b := getI()-1, getI()-1
		node[a] = append(node[a], b)
		node[b] = append(node[b], a)
	}

	dist = make([]int, N)
	used = make([]bool, N)
	xx = make([]int, N)
	dfs(S, p[S], 0, 0)
	t := dist[T]
	x := xx[T]

	ans := t
	for {
		dist = make([]int, N)
		used = make([]bool, N)
		xx = make([]int, N)
		dfs(T, x, t, 1)
		if dist[T] == ans {
			break
		}
		ans = max(ans, dist[T])
	}
	// out(dist, xx)
	// out(t, x)
	out(ans)
}