How about just a formula?

Row\Col
A
B
C
2
1
1
 B2: =IF(A2=1, 1, B1+1)
3
0
2
4
0
3
5
0
4
6
1
1
7
0
2
8
1
1
9
0
2
10
0
3
11
1
1
12
1
1
13
0
2
14
0
3
15
0
4
16
0
5