#include<stdio.h>
int main(){
    int a,b,c,d,e;
    scanf("%d %d %d %d",&a,&b,&c,&d);
    e=c%b;
    switch (e) {
        case 0: if ((c / b-1) * d < a) {printf("Yes");}
            else printf("No");
            break;
        default:   if ((c / b) * d >= a) {
            printf("No");
        } else printf("Yes");
    }
    return 0;
}