How to group data based on another table?

Question

SQL Server

Good day!
There was a task to group the data on the basis of other table.
Given 2 tables.
First (for each x, its pair of y is given):

Second:

In the end, you need to get the sum of Int by comparing/grouping x and y, as they are indicated in the first table. Moreover, there is not always a pair for x and y. That is, you need to get: