fun main() {
    val mod=1000000007
    val n = readLine()!!.toInt()
    val A = IntArray(n)

    for (i in 0..n-1){
        val x = readLine()!!.toInt()
        if (x<n){
            A[x]+=1
        }
    }

    val DP = LongArray(n+1){0}
    DP[0]=1

    for (v in A){
        if (v==0){
            continue
        }
        for (i in 0..n-1){
            var j=n-1-i
            DP[j+1]=(DP[j+1]+DP[j]*v)%mod
        }
    }

    var ANS=0.toLong()
    var fac=1.toLong()
    for (i in 0..n){
        if (i%2==0){
            ANS+=fac*DP[n-i]
            ANS%=mod}
        else{
            ANS-=fac*DP[n-i]}

        fac=fac*(i+1)%mod}

    if (n%2==1) {
        println((-ANS) % mod)
    }
    else{
        println(ANS)
    }
}