March, 8.
Wikipedia:
International Women's Day (IWD) is marked on the 8th of March every year. It is a major day of global celebration of women. In different regions the focus of the celebrations ranges from general celebration of respect, appreciation and love towards women to a celebration for women's economic, political and social achievements.
... Demonstrations marking International Women's Day in Russia proved to be the first stage of the Russian Revolution of 1917.
Following the October Revolution, the Bolshevik feminist Alexandra Kollontai persuaded Lenin to make it an official holiday...
Kollontai ... believed that true socialism could not be achieved without a radical change in attitudes to sexuality, so that it might be freed from the oppressive norms that she saw as a continuation of bourgeois ideas about property...
Cheers!