#include <stdio.h>
//a atac taka
//b forca taka
//atac aoki
//forca aoki
int main(){
    int a,b,c,d;
    int saude1,saude2;


    scanf("%d %d %d %d",&a,&b,&c,&d);

    while(a>0 && c>0){
        c = c - b; //tirando vida do aoki
        a = d - a; //tirando vida do taka
        break;


    }
    if(a>0){
        printf("Yes\n");
    }if(c>0) {
        printf("No\n");
    }






    return 0;
}
