#include <stdio.h>
#include <stdlib.h>
#include <string.h>


int main(){
    int a,b,c,d;
    char token[1000];
    fgets(token, sizeof(token), stdin);
    a=atoi(strtok(token," "));b=atoi(strtok(NULL, " "));
    c=atoi(strtok(NULL, " "));d=atoi(strtok(NULL, " "));
    while (a>0&&c>0) {
        c-=b;a-=d;
    }
    if (a<=0&&c>0) printf("No");
    else if(a>0&&c<=0) printf("Yes");
    else printf("Yes");
    return 0;
}
