Not counting duplicate data

I need a querybuilder query that calculates how many different people the user is messaging without counting the repetitive data.

database photo

Example:

conver_user_id = 165, conver_user_seller_id = 156
conver_user_id = 165, conver_user_seller_id = 156
conver_user_id = 165, conver_user_seller_id = 156
conver_user_id = 165, conver_user_seller_id = 158
conver_user_id = 165, conver_user_seller_id = 158

the result i want : Total count: 2

I will be glad if you help me thank you

via Chebli Mohamed