The Greek Navy was relatively modern, strengthened by the recent purchase of numerous new units and undergoing reforms under the supervision of a British mission. Invited by Prime Minister Venizelos in 1910, the mission began its work upon its arrival in May 1911. Granted extraordinary powers and led by Vice Admiral Lionel Grand Tufnell, it thoroughly reorganized the Navy Ministry and dramatically improved the number and quality of exercises in gunnery and fleet maneuvers. In 1912, the core unit of the fleet was the fast armoured cruiser Georgios Averof, completed in 1910 and, at that time, the fastest and most modern warship in the combatant navies. It was complemented by three rather antiquated battleships of the Hydra class. There were also eight destroyers built in 1906-1907, and six new destroyers that were hastily bought in summer 1912 as the imminence of war became apparent. Nevertheless, at the outbreak of the war, the Greek fleet was far from ready. The Ottoman battlefleet retained a clear advantage in number of ships, speed of the main surface units and, more importantly, in the number and caliber of the ships' guns. In addition, as the war caught the fleet in the middle of its expansion and reorganization, fully a third of the fleet  only reached Greece after hostilities had started, forcing the navy to reshuffle crews, who consequently suffered from lacking familiarization and training time. Coal stockpiles and other war stores were also in short supply, while the Georgios Averof had arrived with barely any ammunition, and would remain so until late November.
Question: How many years before the Prime Minister Venizelos in 1910 was invited until he began his mission in 1911?
Answer: 1