'use strict'

function main(input) {
    const k = Number(input.split('\n')[0].split(' ')[0]);
    const a = Number(input.split('\n')[1].split(' ')[0]);
    const b = Number(input.split('\n')[1].split(' ')[1]);
    for (let index = a; index <= b; index++) {
        if (index % k === 0) {
            console.log('OK');
            return;
        }
    }
    console.log('NG');
}

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