function bulkPreallocate(address[] _owners, uint256[] _tokens, uint256[] _paid)
    public
    onlyOwner() {
        require(
            _owners.length == _tokens.length,
            "Lengths of parameter lists have to be equal"
        );
        require(
            _owners.length == _paid.length,
            "Lengths of parameter lists have to be equal"
        );
        for (uint256 i=0; i< _owners.length; i++) {
            preallocate(_owners[i], _tokens[i], _paid[i]);
        }
    }