#include <stdio.h>


int main()
{

    int s,w;
    scanf("%d %d", &s,&w);
    int c, d;
    scanf("%d %d", &c, &d);

    while(s>=0&&c>=0){

        c = c - w;
        if (c <= 0)
        {
            printf("Yes");
            break;
        }

        s=s - d;
        if(s<=0){
            printf("No");
            break;
        }
    }


    printf("\n");
}