#include <stdio.h>
int main() {
  int A,B,C,D;
  scanf("%d %d %d %d", &A, &B, &C, &D);
  while (1)
  {
      C = C - B;
      if(C <= 0){
          printf("Yes");
          break;
      } 
      A = A - D;
      if(A <= 0){
          printf("No");
          break;
      } 
  }
  return 0;
}