#include<stdio.h>

int main(void)
{
  int A, B, C, D, counter = 0;

  scanf("%d %d %d %d", &A, &B, &C, &D);

  while(A > 0 && C > 0){
    if(counter % 2 == 0){
      C -= B;
    }else{
      A -= D;
    }
    counter ++;
  }

  if(A <= 0){
    printf("No\n");
  }else{
    printf("Yes\n");
  }

  return 0;
}