```sql
WITH NumberedRows
AS (SELECT [Group],
[Index],
Row_number()
OVER (
PARTITION BY [Group]
ORDER BY [Index]) AS RowNumber
FROM Users)
SELECT [Group],
[Index],
( ( RowNumber - 1 ) / 2 ) + 1 AS NewIndex
FROM NumberedRows
ORDER BY [Group],
RowNumber;
```
