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