Try to reverse the cells on data stack: e.g. from 1 2 3 4 5 to 5 4 3 2 1.

Allowed operations:

• swap ( n1 n2 -- n2 n1 ) swap first two elements on data stack
• 2swap ( n1 n2 n3 n4 -- n3 n4 n1 n2 ) swap first four elements on data stack
• >r ( x -- ) ( R: -- x ) move top of data stack to return stack
• r> ( -- x ) ( R: x -- ) move top of return stack to data stack