#include<stdio.h>

int main(void){

    int a,b,c,d;
    scanf("%d %d %d %d",&a,&b,&c,&d);
    // printf("%d %d %d %d\n",a,b,c,d);

    int i=1;
    while (i<=100){
        c=c-b;
        if (c<=0){
            printf("Yes");
            return 0;
        }
        a=a-d;
        if (a<=0){
            printf("No");
            return 0;
        }
        i=i+1;
    }
    

    return 0;
}