#include <stdio.h>
int main(void){
    // Your code here!
    int A, B, C, D;
    scanf("%d %d %d %d", &A, &B, &C, &D);
    if ((C + B - 1) / B > (A + D - 1) / D)
        printf("No");
    else
        printf("Yes");
    return (0); 
}
