#include<stdio.h>

int main(){
	int A, B, C, D;
	scanf("%d %d %d %d", &A, &B, &C, &D);

	while (1){
		A = A - D;
		C = C - B;

		if (A <= 0 || C <= 0) break;
	}
		if (C <= 0){
			printf("Yes\n");
		}
		else{
			printf("No\n");
		}
	return 0;
}