#include <stdio.h>

int main(void){
    int a,b,c,d;
    scanf("%d%d%d%d",&a,&b,&c,&d);
    while(a>=0 && c>=0){
        c -= b;
        if(c <= 0)
            printf("Yes\n");
        a -= d;
        if(a <= 0)
            printf("No\n");
    }
    return 0;
}
