#include <stdio.h>

int main(void)
{
    int C, D;
    int TAKA, AOKI;

    scanf("%d %d %d %d", &TAKA, &AOKI, &C, &D);

    while(TAKA >= 0 && AOKI >= 0){
        AOKI -= C;
        TAKA -= D;
    }
    if (TAKA <= 0)
    {
        printf("No\n");
    }else
    {
        printf("Yes\n");
    }

    return 0;
}