#include <stdio.h>

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

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

    while(TAKA > 0 && AOKI > 0){
        AOKI -= C;
        TAKA -= D;
    }

    if (AOKI <= 0)
        printf("Yes\n");
    else
        printf("No\n");

    return 0;
}