Count calculation result

Hello

I'm trying to count the result of a calculated measure but i'm stucked...

I have 2 distinct tables (with many other differents columns, extracted from 2 differents "tools"), looking like that (simplified version) :

Table 1 : 

id      Amount

1       5

2       10

3       8

Table 2 :

id      Amount

1       5

2       2

3       8

From that, 3 calculated measure :

- based on table 1, SUM(amount) by id (let's call it "sum1")

- based on table 2, SUM(amount) by id (let's call it "sum2")

- based on the 2 previous measure, a "sum3" =  "sum2" - "sum1"

The final results by id is :

id      Amount

1       0

2       -8

3       0

From that, i'm trying to count the number of time where the result is = 0 (2 times in my case).

How can I obtain this result ?