#include <stdio.h>

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

	for (int turns = 0; ; turns++){
		
		//Mr.Takahashi's Attack
		C -= B;
		
		if (C <= 0) {
			printf("Yes");
			break;
		}
		
		
		//Mr.Aoki's Attack
		A -= D;
		
		if (A <= 0) {
			printf("No");
			break;
		}
	}
	
	return 0;
}