int main()
{
    int th, ts, ah, as;
    scanf("%d %d %d %d", &th, &ts, &ah, &as);
    
    int count = 1;
    while(th > 0 && ah > 0){
        if(count % 2 == 1)
            ah = ah - ts;
        else
            th = th - as;
        count ++;
    }
    if(th <= 0)
        printf("No\n");
        
    else
        printf("Yes\n");
}