A given topic is an inevitable event.

( 1+ 1+ 1)+ 1=3+ 1=4, 1+ 1=2

It's okay to touch two pictures from the same country, but it doesn't meet the problem that two pictures belong to two countries.

If you touch three, two of them are from the same country, and 1 is from another country, that's fine, but if three belong to three countries, that's not a problem.

On the premise that three pieces belong to three countries, touch one more 1. No matter which country it belongs to, it must be added with 1 pieces in the original 1 countries to form two pieces.

Therefore, if you touch at least four stamps, then there must be two stamps from the same country.

At first glance, this problem belongs to probability theory, but if it is solved by probability theory, it will fall into a misunderstanding. This problem is solved by the pigeon hole principle.