I have a small dataset and it just has 2 variables. ID---student ID, exam_times----how many times a student took.
I want to use Stata code to find how many students took more than 1 time exam?
Thank you.

clear
input str10 id byte exam_times
1 1
1 2
2 1
3 1
3 2
3 3
3 4
4 1
4 2
4 3
end