private static async Task <IDictionary <string, decimal> > GetSymbolPriceAsync(IEnumerable <string> symbols, AlphaVantageClient client) { var dict = new Dictionary <string, decimal>(); foreach (var symbol in symbols) { await Task.Delay(1000); dict.Add(symbol, (await client.GetQuoteDataAsync(symbol))?.Price ?? throw new ArgumentException($"No data for symbol: {symbol}")); } return(dict); }