#include<stdio.h>
#include<math.h>
#include<string.h>
#include<ctype.h>
#include<stdlib.h>
#define STR 100
int main(){
    int a,b,c,d;
    scanf("%d %d %d %d",&a,&b,&c,&d);
    while(a<=0 || c<=0){
        a-=d;
        c-=b;
    }
    if(c<=0){
        printf("Yes")
    }else{
        printf("No");
    }
    return 0;
}