Which city in the Midwest region has the least number of clients?
least number of clients refers to min(count(client_id))
SELECT T2.city FROM client AS T1 INNER JOIN district AS T2 ON T1.district_id = T2.district_id INNER JOIN state AS T3 ON T2.state_abbrev = T3.StateCode WHERE T3.Region = 'Midwest' GROUP BY T2.city ORDER BY COUNT(T2.city) LIMIT 1