exceptionally allow the offender to leave the premises of house detention for a definite period of time, when it is absolutely necessary to ensure vital necessities of life, medical assistance, or to perform work. If the offender leaves the building of house detention without the court’s prior consent or outside allowed time, the court may decide that the imposed sentence of imprisonment shall be executed. (4) The sentence of imprisonment may also be implemented so that the offender in the period of maximum two years performs community service in the amount of minimum eighty and maximum four hundred and eighty hours. The community service shall be distributed in a way not to disturb the offender's obligations of his employment relationship. Such form of implementation shall be decided by the court, which ordered the sentence at the first instance, considering the objective and subjective circumstances of the perpetrator and his consent with this kind of implementation of the sentence. The sentence of imprisonment, which was imposed on the perpetrator for the criminal offence against sexual inviolability, cannot be substituted by community service. If the offender does not fulfil the tasks arising from performing community service, the court may order the execution of the sentence of imprisonment. Method of Execution of Fines Article 87 (1) If a fine cannot be forcibly collected, the court shall execute it so that one day of imprisonment shall be ordered for two daily instalments of the fine, whereby the imprisonment may not be longer than six months. (2) If the offender pays only part of the fine, the remaining part shall be proportionately converted into days of imprisonment; however, if the remaining part is paid, the execution of the sentence of imprisonment shall be discontinued. (3) If the offender dies, the fine shall not be executed. Release on Parole Article 88 (1) The offender, who has served half of his sentence of imprisonment, may be released from a penal institution under the condition that until the term, for which he was sentenced, has elapsed he does not commit another criminal offence. (2) The offender, who has been sentenced to over fifteen years' imprisonment, may be released on parole after he has served three quarters of the sentence. (3) The offender, who has been sentenced to life imprisonment, may be released on parole after he has served twenty-five years in prison.