#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");
            break;
        }
        A -= D;
        if (A <= 0)
        {
            printf("No");
            break;
        }
    }
    return 0;
}