#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 = a - d; //tirando vida do taka
    }
    
    if(c<=0){
        printf("Yes\n");
    } else {
        printf("No\n");
    }

    return 0;
}

