According to the Art. Art. 80, 81 of the Family Code of Russia, the parents shall be obliged to maintain their minor children. If the parents do not provide maintenance to their minor children, the means for maintaining the minor children (the child support) shall be exacted from the parents through court. The child support for the minor children shall be exacted by the court from their parents monthly earnings in the amount of one fourth of the parents' earnings and (or) of another kind of income for one child, one third - for two children, and half of the parents' earnings and (or) other income - for three or more children. The amount of these shares may be reduced or increased by the court with account for the material situation or the family status of the parties, and also for other circumstances worthy of attention.

I am going to use Art. 83 of the Family Code of Russia. According to this article, if there is no parents' agreement on the payment of child support for minor children, and if the parent obliged to pay the child support, has irregular or changing earnings and (or) other income, or if this parent receives these earnings and (or) other income fully or in part in kind or in foreign currency, or if he has no earnings and (or) other income, and also in other cases, if the exaction of the child support as a share of the parent's earnings and (or) other income is impossible, difficult or essentially infringes upon the interests of one of the parties, the court shall have the right to define the amount of the child support, to be exacted monthly, as a fixed monetary amount. The size of the fixed monetary amount shall be defined by the court, proceeding from an attempt to ensure to the maximum possible extent the child's former maintenance level, taking into account the material situation and the family status of the parties and other circumstances worthy of attention.