#include <stdio.h>

int main(void)
{
    int a=0,b=0,c=0,d=0,count=0;
    scanf("%d %d %d %d",&a,&b,&c,&d);

    while(count!=100){
        c-=b;
        if(c<=0){
            printf("Yes");
            break;
        }
        a-=d;
        if(a<=0){
            printf("No");
            break;
        }
        count+=1;
    }

    return 0;
}
