German ostruble
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Ostruble is the name given to a currency denominated in kopek and ruble, which was issued by Germany in 1916 for use in the eastern areas under German occupation. It was initially equal to the Russian ruble.
From 1918, it circulated alongside the ostmark in some places, with 1 ostmark = 2 ostruble. It circulated in Lithuania until 1922, when it was replaced by the litas.