title: Observable<List<SomeItems> from multiple retrofit requests
body: <p>I get Flowable from retrofit request. 
  I need to get from multiple requests one Object like Observable> in while construction: </p>
  
  <pre><code>public static Observable&lt;List&lt;CurrencyStamp&gt;&gt; getStampByDay(String symbol, Date date, String... convertsSymbols){
          long count = 0;
  
          Observable&lt;List&lt;CurrencyStamp&gt;&gt; result = null;
          while (count &lt; secByDay){
              Flowable&lt;CurrencyStamp&gt; item = CoinApi.getCompareApi().getCurrencyHistory(symbol, date.getTime() - count,
                      convertsSymbols).subscribeOn(Schedulers.io())
                      .observeOn(AndroidSchedulers.mainThread());
  
  
              count += secByFiveMin;
          }
  
  
          return result;
      }
  </code></pre>
  
  <p>Which operators i need?</p>