Soviet troops  approached the Lithuanian territory on December 12, 1918. About 5,000 of them were Lithuanians. Three divisions were employed: Pskov division , International Division , and 17th Division . The divisions did not have a common military commander. Later more units were sent from Russia. The soviets also recruited partisan groups behind the front lines. Soviet soldiers were poorly supplied and had to support themselves by requisitioning food, horses, and clothes from local residents. Lithuania could not offer serious resistance as at the time its army consisted only of about 3,000 untrained volunteers. Only local partisans, armed with weapons acquired from retreating Germans, offered brief resistance. Red Army captured one town after another: Zarasai and Švenčionys , Utena , Rokiškis , Vilnius , Ukmergė and Panevėžys , Šiauliai , Telšiai . That accounted for about ⅔ of the Lithuanian territory. The front somewhat stabilized when Soviet forces were stopped near the Venta River by Latvian and German units . Also Germans slowed down withdrawal of their troops after the Spartacist uprising was subdued on January 12. Southern Lithuania was a little better protected as Germans retreated from Ukraine through Hrodna. To prevent fights between retreating Germans and the Red Army, the Soviets and Germans signed a treaty on January 18. The treaty drew a temporary demarcation line that went through Daugai, Stakliškės, and 10 kilometres  east of Kaišiadorys-Jonava-Kėdainiai railway. That barred Bolshevik forces from directly attacking Kaunas, Lithuania's second-largest city. The Red Army would need to encircle Kaunas and attack through Alytus or Kėdainiai. The operation to take Kaunas began on February 7.

Based on the above article, answer a question. How many months after Soviet troops approached the Lithuanian territory did the operation to take Kaunas begin?
2