var [A, B, C, D] = require('fs').readFileSync('/dev/stdin', 'utf8').split(' ').map(Number)
var ans
while (true) {
  C -= B
  if (C <= 0) {
    ans = 'Yes'
    break
  }
  A -= D
  if (A <= 0) {
    ans = 'No'
    break
  }
}
console.log(ans)