#include<stdio.h>
#include<math.h>
#include<stdlib.h>


int main(){
    int a, b, c, d;
    scanf("%d %d %d %d", &a, &b, &c, &d);
    int eqt=a, eqa= c;

    for(;;){
        eqa-=b;
        if(eqa<=0){
            printf("Yes\n");
            break;
        }

        eqt-=d;
        if(eqt<=0){
            printf("No\n");
            break;
        }


    }
}