8 08.11

private infix fun Boolean.arrow(other: Boolean) = !(this && !other)

fun main() {
    var cnt = 0
    val letters = listOf('K', 'P', 'O', 'B', 'I')

    letters.forEach { f ->
        val l1 = letters - f

        l1.forEach { s ->
            val l2 = l1 - s

            l2.forEach { t ->
                val l3 = l2 - t

                l3.forEach { fo ->
                    val l4 = l3 - fo

                    l4.forEach { fi ->
                        "$f$s$t$fo$fi"
                            .takeIf { it.first() != 'I' && "IO" !in it && "OI" !in it }
                            ?.let { cnt++ }
                    }
                }
            }
        }
    }

    println(cnt)
}