#include <stdio.h>
#include <stdlib.h>
 
int main(void){
    int i,j,k,l;
    scanf("%d %d %d %d", &i,&j,&k,&l);
    while(1){
    k-=j;
    if(k<1){printf("Yes");return 0;}
    i-=l;
    if(i<1){printf("No");return 0;}
    }
  return 0;
}