There are 20 Canadians and 20 Americans at the conference.
we met the first person may be Canadian or American
Case 1:
If the first person is Canadian
We meet the second person
The second person also maybe Canadian or American
If all the first 20 peoples are Canadian
The next two people should be American
Hence we should meet a minimum of 22 people.
Case 2:
If the first person is American
We meet the second person
The second person also maybe Canadian or American
If all the next 20 peoples are Canadian
Then the 22nd people should be American
Hence we should meet a minimum of 22 people.
Case 3:
If the first person is American
We meet the second person
The second person also maybe Canadian or American
If the second people is also American
Hence we met 2 Americans in two attempts.
Result:
We need to meet 22 people to meet two americans.