#include<stdio.h>
int main(void)
{
    int a,b,c,d,i;
    scanf("%d %d",&a,&b,&c,&d);

    while(1){
        c=c-b;
        if(c<=0){
            printf("Yes\n");
            break;
        }
        a=a-d;
        if(a<=0){
            printf("No\n");
            break;
        }
    }

    return 0;
}