def get_position(row_index, col_index, board_size):
    """ (int, int, int) -> int
    
    Precondition: 0 < row_index <= board_size and
                  0 < col_index <= board_size and
                  1 <= board_size <= 9
    
    Return the str_index of the cell in the string representation 
    of the game board corresponding to the given row and column indices.
    
    >>> get_position(2, 1, 4)
    4
    >>> get_position(3 ,1, 3)
    6
    """
    
    return (row_index - 1) * board_size + col_index - 1