#include<stdio.h>

int main(void){
    int Thp,Tat,Ahp,Aat;
    
    scanf("%d %d %d %d ",&Thp,&Tat,&Ahp,&Aat);
    while((Thp>0)||(Ahp>0)){
        Ahp=Ahp-Tat;
        if(Ahp>0){
            Thp=Thp-Aat;
        }
    }
    if(Ahp<=0){
        printf("Yes\n");
    }
    else if(Ahp>0){
        printf("No\n");
    }
    return 0;
}