#include <stdio.h>

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

    for (int a = A, c = C;;)
    {
        c -= B;
        if (c <= 0)
        {
            printf("Yes");
            break;
        }
        a -= D;
        if (a <= 0)
        {
            printf("No");
            break;
        }
    }
    return 0;
}