function main(input){
  input = input.split('\n');
  const [A, B, C, D] = input[0].split(' ').map(Number);

  const ret = (Math.ceil(C/B) > Math.ceil(A/D))?
    'No' : 'Yes'

  console.log(ret)
}
main(require('fs').readFileSync('/dev/stdin', 'utf8').trim());
