#include <stdio.h>
int main(void)
{
int A,B,C,D;
scanf("%d",&A);
scanf("%d",&B);
scanf("%d",&C);
scanf("%d",&D);
while(A>0&&C>0)
{
C=C-B;
A=A-D;
if(C<=0)
A=A+D;
}
if(A<=0)
printf("No");
else
printf("Yes");
return 0;
}