getmin in stack in o(1) time

You need to design a stack which holds an integer value such that getMinimum() function should return the minimum element in the stack.
For example: consider the below example

case #1

5  --> TOP
1
4
6
2

When getMinimum() is called it should return 1, which is the minimum element 
in the stack. 

case #2

stack.pop()
stack.pop()

Note: Both 5 and 1 are poped out of the stack. So after this, the stack
looks like,

4  --> TOP
6
2

When getMinimum() is called is should return 2 which is the minimum in the 
stack.

Note: 1. Design it without using another stack,you can change the structure of stack node.
2. Design it using extra stack.