#include<stdio.h>

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