Good Day!

I am currently trying to reshape the Bruegel Dataset. Currently it is comprised of a year variable and several country variables as columns (see below):

Period Australia Austria ....... Vietnam
1996 XXX XXX XXX
1997 XXX XXX XXX
1998 XXX XXX XXX
1999 XXX XXX XXX
2000 XXX XXX XXX

*Note that XXX are actual values.

I am trying to reshape the data wherein countries would be a new variable (see below):
Period Country Exchange Rate
1996 Australia XXX
1996 Austria XXX
1996 Vietnam XXX
1997 Australia XXX
1997 Austria XXX
1997 Vietnam XXX

Since there would be two new variable, what would be the best command to perform this? Thank you!