#include<stdio.h>
int main(void){
    int a,b,c,d;
    scanf("%d %d %d %d",&a,&b,&c,&d);
    int taka=a,aoki=c;
    while(1){
        aoki=aoki-b;
        taka=taka-d;
        if(aoki<=0 && taka>0){
            printf("Yes\n");
            break;
        }else if(taka<=0 && aoki>0){
            printf("No\n");
            break;
        }else{
          continue;
        }
    }
    return 0;
}