ANDREJEVA v. LATVIA JUDGMENT 19 also pointed out that the applicant’s monthly pension had been recalculated ex nunc and not ex tunc. In other words, it was only with effect from 2000 that she had begun to receive the exact amount corresponding to the “Ukrainian” period of her career, and no payments had been made to her retrospectively. However, the Government submitted that that position complied with Article 28 of the 1969 Vienna Convention on the Law of Treaties, which laid down the general principle that international treaties did not have retrospective effect “[u]nless a different intention appears from the treaty or is otherwise established”; that had not been the case in this instance. In any event, the Government submitted that the difference between the amount of the pension currently received by the applicant and the amount she would receive if her pension were recalculated with retrospective effect was minimal and not capable of imposing an “excessive financial burden” on her. 48. The applicant acknowledged that, after the agreement with Ukraine had been concluded, the amount of her pension had been recalculated and slightly increased. However, the agreement did not contain any clause allowing the corresponding portion of her “Ukrainian” pension to be paid retrospectively. That also applied to other social security agreements, including the one with the Russian Federation which had just been approved and was due to take effect soon. 49. The Court points out that by Rule 55 of the Rules of Court, “[a]ny plea of inadmissibility must, in so far as its character and the circumstances permit, be raised by the respondent Contracting Party in its written or oral observations on the admissibility of the application”. In the instant case, it notes that the pension in issue was recalculated in 2000; accordingly, there was nothing to prevent the Government from raising their objection at the admissibility stage. Having failed to do so, they are estopped from relying on it. In the light of these considerations, while acknowledging that the issue raised by the Government is relevant in relation to Article 41 of the Convention (see paragraph 104 below), the Court cannot allow this objection. 50. Furthermore, the Court takes note of the recent approval by the parliaments of the two States concerned of the cooperation agreement between the Russian Federation and Latvia on social security (see paragraphs 44-45 above). However, irrespective of what benefit the applicant might draw from that agreement after it comes into force, the Court observes that the situation complained of remains unchanged to date. It thus has no reason to consider that the applicant’s status as a “victim” within the meaning of Article 34 of the Convention has thereby been affected.