/* B - Battle */

#include <stdio.h>

int main(void){
  int A, B, C, D,takahashi = 1, aoki = 0;
  scanf("%d %d %d %d", &A, &B, &C, &D);
  while(A > 0 && C > 0){
    if(takahashi == 1 && aoki == 0){
      C -= B;
      takahashi = 0;
      aoki = 1;
    }else{
      A -= D;
      takahashi = 1;
      aoki = 0;
    }
  }

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

  return 0;
}
