"use strict";

function main(input) {
  input = input.split("\n");
  let tmp = input[1].split(" ");
  let a = parseInt(tmp[0]);
  let b = parseInt(tmp[1]);
  for (a; a <= b; a++) {
    const res = a % parseInt(input[0]);
    if (res === 0) {
      console.log("OK");
      return;
    }
  }
  console.log("NG");
}

main(require("fs").readFileSync("/dev/stdin", "utf-8"));
