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