import java.io.PrintWriter import java.util.* import kotlin.math.* fun PrintWriter.solve() { val n = nextInt() val a = Array(n) { nextInt() } a.reverse() val l = (0 until n).map { i -> a[i] + n - i } var numer = ModInt(1) var denom = ModInt(1) for (i in 0 until n) { for (j in i + 1 until n) { numer *= ModInt(l[i] - l[j]) denom *= ModInt(j - i) } } val ssyt = numer / denom println(ssyt * ssyt) } // region ModInt class ModInt(x: Long) { companion object { const val MOD = 998244353L //const val MOD = 1000000007L } constructor(y: Int) : this(y.toLong()) val x = (x % MOD + MOD) % MOD operator fun plus(other: ModInt): ModInt { return ModInt(x + other.x) } operator fun minus(other: ModInt): ModInt { return ModInt(x - other.x) } operator fun times(other: ModInt): ModInt { return ModInt(x * other.x) } operator fun div(other: ModInt): ModInt { return this * other.inv() } fun pow(exp: Long): ModInt { if (exp == 0L) return ModInt(1L) var a = pow(exp shr 1) a *= a if (exp and 1L == 0L) return a return this * a } fun inv(): ModInt { return this.pow(MOD - 2) } override fun equals(other: Any?): Boolean { if (this === other) return true if (javaClass != other?.javaClass) return false other as ModInt if (x != other.x) return false return true } override fun hashCode(): Int { return x.hashCode() } override fun toString(): String { return "$x" } } class ModIntArray(n: Int) { private val a = LongArray(n) { 0L } constructor(n: Int, init: (Int) -> ModInt) : this(n) { for (i in 0 until n) { a[i] = init(i).x } } operator fun set(i: Int, x: ModInt) { a[i] = x.x } operator fun get(i: Int): ModInt { return ModInt(a[i]) } fun joinToString(s: String = ", "): String { return a.joinToString(s) } } fun Long.toModInt() = ModInt(this) fun Int.toModInt() = ModInt(this) fun binomSimple(n: Long, k: Long): ModInt { var numer = ModInt(1) var denom = ModInt(1) for (i in 0 until k) { numer *= ModInt(n - i) denom *= ModInt(k - i) } return numer / denom } // endregion fun main() { Thread(null, { val writer = PrintWriter(System.out, false) writer.solve() writer.flush() }, "solve", abs(1L.shl(26))) .apply { setUncaughtExceptionHandler { _, e -> e.printStackTrace(); kotlin.system.exitProcess(1) } } .apply { start() }.join() } // region Scanner private var st = StringTokenizer("") private val br = System.`in`.bufferedReader() fun next(): String { while (!st.hasMoreTokens()) st = StringTokenizer(br.readLine()) return st.nextToken() } fun nextInt() = next().toInt() fun nextLong() = next().toLong() fun nextLine() = br.readLine() fun nextDouble() = next().toDouble() // endregion