Consecutive flags in consecutive cycles

[Paakay]

I have ID's with multiple flags in cycles however some id's flags are not consecutive. For example ID A has two flags in cycle 1 but none in cycle 2,3,4 but then has another flag in cycle 5. I want to keep only the flags in cycle 1 and delete flags in cycle 5 since there is a break in cycle at 2. Another example is ID B has flags in cycles 1, 2,3 but not in cycle 4 however has flags in cycles 5 and 6. Since there is a break in cycle at 4, I want to keep the consecutive flags in cycles 1,2,3 and delete cycles 5 and 6. Can someone help me with this. Sample data is below

DATA chk;
   INPUT  ID $  Flag Cycle ;
CARDS;
A 1 1
A 1 1
A 1 5
A 1 5
B 1 1
B 1 2
B 1 3
B 1 5
B 1 6
C 1 1
C 1 1
C 1 2
C 1 4
C 1 5
;
RUN;

This is the output I want

         ID.     FLG  CYC

1

A

1

1

2

A

1

1

3

B

1

1

4

B

1

2

5

B

1

3

6

C

1

1

7

C

1

1

8

C

1

2

[ChrisNZ]

Like this?

data HAVE;
  input ID $ FLAG CYCLE ;
cards;
A 1 1
A 1 1
A 1 5
A 1 5
B 1 1
B 1 2
B 1 3
B 1 5
B 1 6
C 1 1
C 1 1
C 1 2
C 1 4
C 1 5
run;

data WANT;  
  set HAVE;
  by ID;
  DEL_FLG= ifn( first.ID           , .
         , ifn( CYCLE>lag(CYCLE)+1 , 1
         , DEL_FLG ));
  if DEL_FLG then delete;
  retain DEL_FLG;
run;