#include<stdio.h>
int main(void){
    int a,b,c,d;
    scanf("%d %d %d %d",&a,&b,&c,&d);
    while(c<=0||a<=0){
        c-=b;
        a-=d;
    }
    if(c<a){
        printf("Yes\n");
    }else{
        printf("No\n");
    }
    return 0;
}