#include<stdio.h>


int main(){
    int A,B,C,D;
    scanf("%d %d %d %d",&A,&B,&C,&D);
    while (1) {
        A-=D;
        if(A<=0){
            printf("No\n");
            return 0;
        }
        C-=B;
        if(C<=0){
            printf("Yes\n");
            return 0;
        }
    }
}
