Answer based on context:

The 11-week Conference of Lausanne was held in Lausanne, Switzerland, during 1922 and 1923. Its purpose was the negotiation of a treaty to replace the Treaty of Sèvres, which, under the new government of the Grand National Assembly, was no longer recognised by Turkey. The conference opened in November 1922, with representatives from the United Kingdom, France, Italy and Turkey. It heard speeches from Benito Mussolini of Italy and Raymond Poincaré of France. At its conclusion, Turkey assented to the political clauses and the "freedom of the straits", which was Britain's main concern. The matter of the status of Mosul was deferred, since Curzon refused to be budged on the British position that the area was part of Iraq. The British Iraq Mandate's possession of Mosul was confirmed by a League of Nations brokered agreement between Turkey and Great Britain in 1926. The French delegation, however, did not achieve any of their goals and on 30 January 1923 issued a statement that they did not consider the draft treaty to be any more than a "basis of discussion". The Turks therefore refused to sign the treaty. On 4 February 1923, Curzon made a final appeal to Ismet Pasha to sign, and when he refused the Foreign Secretary broke off negotiations and left that night on the Orient Express.

How many countries opened the Conference of Lausanne?
4