investigation or trial, due to a change of situation, the act committed by that person has lost its socially dangerous nature or that person has ceased to be dangerous to the public. Article 49. Discharge from criminal liability due to limitation period 1. A person shall be discharged from criminal liability if the following periods have elapsed from the date of the criminal offense to the effective date of the judgment: (1) two years where a minor offense has been committed and the prescribed punishment is less severe than the restraint of liberty; (2) three years where a minor offense has been committed and the prescribed punishment is the restraint of liberty or imprisonment; (3) seven years where an offense of medium gravity has been committed; (4) fifteen years where a grave offense has been committed; (5) twenty years where a special grave offense has been committed. 2. The statute of limitations shall be saved where a person who committed a criminal offense evaded investigation or trial. In such cases the running of the statute of limitations is resumed as of the date of the person's surrender or apprehension. In this case the person shall be discharged from liability if twenty years elapsed after the commission of the offense. 3. The statute of limitation shall be forfeited where a person, before the terms specified in paragraphs (1) and (2) of this Article have expired, commits another medium grave, grave or special grave offense. In this case a limitation period starts on the date on which such new crime is committed. Each offense gives rise to its own period of limitation. 4. Where a person has committed a special grave offense punishable by life imprisonment, the issue of limitation shall be decided by a court. Where a court rules out the possibility to apply a period of limitation, a sentence of life may not be imposed and is commuted to an imprisonment for a determinate term. 5. The statute of limitation shall not apply where any crime against the peace and humanity, as provided for in Articles 437 through 439, and paragraph 1 of Article 442 of this Code. Chapter X. PUNISHMENT AND ITS TYPES Article 50. The definition of punishment and its purpose 1. The punishment is a coercive measure imposed in a judgment of court on behalf of the State upon a person found guilty of a criminal offense and consists in restraint of the sentenced person's rights and freedoms secured by law. 2. The punishment is aimed not only at penalizing but also reformation of sentenced persons and prevention of further offenses by both the sentenced and other persons. 3. The punishment is not meant to cause physical sufferings or humiliate human dignity. Article 51. Types of punishment 1. The following types of punishment may be imposed by a court on persons convicted of criminal offenses: