#include <stdio.h>
int a,b,c,d,i,j,k;
int main(void){
        scanf("%d %d %d %d",&a,&b,&c,&d);
        for(;;){
                c = c - b;
          		if(c < 1){
                        printf("Yes");
                  		return 0;
                }
          		a = a - d;
                if(a < 1){
                        printf("No");
                  		return 0;
                }
        }
}
