#include <stdio.h>
 
int main(void) {
 
int A, B, C, D;
 
scanf("%d %d %d %d", &A, &B, &C, &D);
 
while (1) {
    C -= B;
    if (C <= 0) {
        printf("Yes\n");
        break;
    }
    A -= D;
    if (A <= 0) {
        printf("No\n");
        break;
    }
}
 
return 0;
 
}