const Main = input => {
  const sp = input.split(' ').map(e => Number(e));

  const a = Math.floor( sp[2] / sp[1] );
  const b = Math.floor( sp[0] / sp[3] );
  const beta = sp[0] % sp[3];

  console.log(( a < b || ( a === b && beta === 0 ) ) ? 'No' : 'Yes' );
};

Main(require('fs').readFileSync('/dev/stdin', 'utf8'));
//Main(`10 9 10 10`);
//Main(`46 4 40 5`)
