#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>


int cmp(const void *a,const void *b){
    if(*(int*)a>*(int*)b){return 1;}
    else if(*(int*)a<*(int*)b){return -1;}
    else {return 0;}
}


int main(void){
int a,b,c,d;
scanf("%d %d %d %d",&a,&b,&c,&d);
for(;;){
    c=c-b;
    if(c<=0){printf("Yes");return 0;}
    a=a-d;
    if(a<=0){printf("No");return 0;}
}

}
