How to append a datarow of a df to another df top row

Question

I have a two df's

df1,
 key count
 one  2
 two  3



 df2,
 key count
 four 5
 five 6

I tried appending but it adds at the end,

My desired output should be,

 df,
 key  count
 one  2
 two  3
 four 5
 five 6