#include <stdio.h>

int main()
{
  int A, B, C, D;
  scanf("%d %d %d %d", &A, &B, &C, &D);
  
  while(1){
    C -= B;
    if(C <= 0){
      printf("Yes\n");
      return 0;
    }
    A -= D;
    if(A <= 0){
      printf("No\n");
      return 0;
    }
  }
  return 0;
}