#include <stdio.h>
int main(void){
    // Your code here!
    int a,b,c,d,k=0;
    scanf("%d%d%d%d",&a,&b,&c,&d);
    while(1){
        c-=b;
        if(c<=0){
            k++;
            break;
        }
        a-=d;
        if(a<=0){
            k+=2;
            break;
        }
    }
    if(k==1)printf("Yes\n");
    else printf("No\n");
    return 0;
}