#include<stdio.h>

int main(void){
    int a,b,c,d;
    scanf("%d %d %d %d",&a,&b,&c,&d);
    while(1){
        c-=b;
        if(c <= 0){
            puts("Yes");
            return 0;
        }
        a-=d;
        if(a <= 0){
            puts("No");
            return 0;
        } 
    }
}