What is the administrator's email address of the chartered school with the fewest students enrolled in grades 1 through 12?
Charted school means `Charter School (Y/N)` = 1 in the table frpm; Students enrolled in grades 1 through 12 refers to `Enrollment (K-12)`
SELECT T2.AdmEmail1 FROM frpm AS T1 INNER JOIN schools AS T2 ON T1.CDSCode = T2.CDSCode WHERE T1.`Charter School (Y/N)` = 1 ORDER BY T1.`Enrollment (K-12)` ASC LIMIT 1