How to keep only the last and the last second observation of a group?

[Shradha1]

I have a liat of students. For each student at a particular tine there is a flag which takes value 0 or 1. The data is sorted in ascending order. Student time flag;
A. 1:20 0
A. 1:35. 1
A 2:40 0
B. 5:30. 0
B. 5:35. 0
B. 6:10. 1

I want to keep only those observations for a student where the flag is 1, and the observation prior to that. Like for this example I want to keep the first two obs for student A and last two for B.
How fo I achieve this? Please help

[PeterClemmensen · Accepted solution]

data have;
input student $ time $ flag;
datalines;
A  1:20  0
A  1:35. 1
A  2:40  0
B  5:30. 0
B  5:35. 0
B  6:10. 1
;

data want;
    merge have 
          have(firstobs = 2 keep = flag rename = flag = f);
    if f or flag;
    drop f;
run;

[Shradha1]

This helped thanks a lot!!