#include<stdio.h>

int main(void) {

	int A, nowA, pastA, B;
	int C, nowC, pastC, D;

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

	nowA = A, pastA = A;
	nowC = C; pastC = C;
  
	while (nowA > 0) {
		nowC = pastC - B;
		pastC = nowC;
		if (nowC <= 0) {
			break;
		}
		nowA = pastA - D;
		pastA = nowA;
	}
	
	if (nowA <= 0) {
		printf("No");
	}
	else if (nowC <= 0) {
		printf("Yes");
	}

	return 0;
}