push_front:3
New Stack: 3
push_back:2
New Stack: 3 2
push_front:4
New Stack: 4 3 2
push_back:5
New Stack: 4 3 2 5
front:4
New Stack: 3 2 5
back:5
New Stack: 3 2
front:3
New Stack: 2
back:2
New Stack:  (*** The program crashes ***)