As many as 50 heads of state including India have been invited to take part in the eleventh session of the United Nations Conference on Trade and Development (Unctad) scheduled to be held in Sao Paulo in Brazil from June 13 to 18. Addressing a news conference here, Director, International Trade in Goods, Services and Commodities, Unctad, Ms Lakshmi Puri, said the organisation meets every four years to set priorities and guidelines for the organisation, besides offering an opportunity to debate key economic and development issues, particularly those relating to trade, investment, finance and technology.