Answer based on context:

Soon after the Battle of Warsaw the Bolsheviks sued for peace. The Poles, exhausted, constantly pressured by the Western governments and the League of Nations, and with its army controlling the majority of the disputed territories, were willing to negotiate. The Soviets made two offers: one on 21 September and the other on 28 September. The Polish delegation made a counteroffer on 2 October. On the 5th, the Soviets offered amendments to the Polish offer, which Poland accepted. The Preliminary Treaty of Peace and Armistice Conditions between Poland on one side and Soviet Ukraine and Soviet Russia on the other was signed on 12 October, and the armistice went into effect on 18 October. Ratifications were exchanged at Liepāja on 2 November. Long negotiations of the final peace treaty ensued. Meanwhile, Petliura's Ukrainian forces, which now numbered 23,000 soldiers and controlled territories immediately to the east of Poland, planned an offensive in Ukraine for 11 November but were attacked by the Bolsheviks on 10 November. By 21 November, after several battles, they were driven into Polish-controlled territory.

How many days after the armistice went into effect did the Bolsheviks attack the Polish?
23