Bad News for you, Japan & Rusia never signed that contract. Kuryles.
Japan and the Soviet Union ended their formal state of war with the Soviet–Japanese Joint Declaration of 1956 but did not sign a peace treaty. During talks leading to the joint declaration, the Soviet Union offered Japan the two smaller islands of Shikotan and the Habomai Islands in exchange for Japan renouncing all claims to the two bigger islands of Iturup and Kunashir, but Japan declined the offer. This disagreement between the two-island offer made by the Soviet Union and Japan's demand of regaining two bigger islands as well became the cornerstone for continuation of the dispute into the present day
