Table schema:
CREATE TABLE table_2518850_4 (year_of_previous_participation VARCHAR, total_number_of_participation VARCHAR, high_school_name VARCHAR)

Question: How many previous years did Maebashi Ikuei high school have a total number of 1 participation?
SQL: SELECT COUNT(year_of_previous_participation) FROM table_2518850_4 WHERE total_number_of_participation = 1 AND high_school_name = "Maebashi Ikuei"