On 28 January the PPS and the Social Democracy of the Kingdom of Poland and Lithuania called for a general strike; over 400,000 workers became involved in strikes all over Poland, a strike that lasted for four weeks. This was only a prelude to an even larger series of strikes that rocked Poland over next year. In the years 1905-1906 close to 7,000 strikes and other work stoppages occurred, involving 1,3 million Poles. Protesters demanded both improved conditions for workers and more political freedom for the Poles. By February, students at Polish universities had joined the demonstrations, protesting russification and demanding the right to study in Polish language. They were joined by high school students and even some from the elementary schools. While the Russian government gave in and agreed to some concessions towards the Polish nationalist movement , many - particularly the workers - were still unsatisfied. In some places in Poland, the school strikes lasted for close to three years. Major demonstrations occurred on May 1 , and about 30 people were shot during a demonstration in Warsaw. Later that month, for a time, public order disintegrated in Warsaw during a spontaneous campaign against the criminal elements as well as Russian collaborators.
Question: How many days did over 400,000 workers become involved in strikes all over Poland?
Answer: 28