I have two dataframes, where I would like to add the another counter column for matching rows between these dataframes rows.

df1:

```
Id   val1  val2   val3
0     ab     ba     sx
1     bc     dc     xy
2.    ab     ba     ux

```

df2:

```
Id   val1  val2   val3
0     ab     ba      zx
1     bc     dc      vy

```

Expected result:
df3:

```
Id   val1  val2   val3  counter
0     ab     ba     sx       1
1     bc     dc     xy      1
2.    ab     ba     ux      2

```

I want here to match the `val1` and `val2` column and add the counter in *df3* for matched rows between these dataframes *df1* and *df2*.

Any help will be much appreciated.