'use strict';
function main(input) {
  const
    arr = input.trim().split('\n'),
    a = Number(arr[0]),
    b = arr[1].split(' ').map(x => Number(x));
  let 
    isPossible = false;

  for (let i = b[0]; i <= b[1]; i ++) {
    if (i % a === 0) {
      isPossible = true;
      break;
    }
  }
  
  console.log(isPossible ? 'OK' : 'NG');
}

main(require('fs').readFileSync('/dev/stdin', 'utf8'));