Sofia is the economic heart of Bulgaria and home to most major Bulgarian and international companies operating in the country, as well as the Bulgarian National Bank and the Bulgarian Stock Exchange. The city and its surrounding Yugozapaden NUTS II planning region is the most developed region in the country. Increasingly, Sofia is becoming an outsourcing destination for multinational companies, among them IBM, Hewlett-Packard, SAP, Siemens, Software AG. Bulgaria Air, PPD, the national airline of Bulgaria, has its head office on the grounds of Sofia Airport. The city has now attracted a cumulative total of $11,6 billion in foreign direct investment.