const main = (str) => {
    const k = str.split('\n')[0];
    const [a,b] = str.split('\n')[1].split(' ');
    if(b-a+1>= +k){
        console.log('OK');
    }else{
        console.log('NG');
    }
};

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