第 + Number + 任 + Title
The measure word 任 (rèn) is used to count terms or tenures of office for officials, leaders, or holders of a title. It is placed between a number and the title to indicate which term the person serves in, such as 第一任总统 (the first president).
他是这所大学的第三任校长。
Tā shì zhè suǒ dàxué de dì sān rèn xiàozhǎng.
He is the third president of this university.
新一任总经理下周正式上任。
Xīn yí rèn zǒngjīnglǐ xià zhōu zhèngshì shàngrèn.
The new general manager will officially take office next week.
她是这个部门历任主任中最年轻的一任。
Tā shì zhège bùmén lìrèn zhǔrèn zhōng zuì niánqīng de yí rèn.
She is the youngest department director among all those who have held the position.