#include <iostream>

int main(int argc, char *argv[]) {
  int a, b, c, d;
  std::cin >> a >> b >> c >> d;
  int i = 0;
  while (a > 0 && c >> 0) {
    if (i % 2 == 0)
      c -= b;
    else
      a -= d;
    ++i;
  }
  if (a>0)
    std::cout << "Yes" << std::endl;
  else
    std::cout << "No" << std::endl;
}
