import Foundation
 
let input_line: String = readLine()!
let split: [String] = input_line.components(separatedBy: " ")
 
let K = Int(split[0])!
let A = Int(split[1])!
let B = Int(split[2])!

if (B - B % K >= A){
    print("OK")
}else{
    print("NG")
}