import java.util.*

fun main() {
    val sc = Scanner(System.`in`)
    val k = sc.nextInt()
    val (a, b) = (0 until 2).map { sc.nextInt() }
    var bdivk = b / k
    if (bdivk * k < a) {
        println("NG")
    } else {
        println("OK")
    }
}