#include<stdio.h>
int main(void){
    int a,b;
    int c,d;
    int count;
    int countt;
    scanf("%d %d %d %d",&a,&b,&c,&d);
    for(count=0;c>0;count++){
        c-=b;
    }
    for(countt=0;a>0;countt++){
        a-=d;
    }
    if(count<=countt){
        printf("Yes\n");
    }else{
        printf("No\n");
    }
    return 0;
}