Stucked in SPOJ GSS1

I have read and implemented segment trees recently and i am trying to solve this problem(GSS1) in spoj but wasn’t able to solve it…Then i read from different sources on internet on how to solve this problem but isn’t able to understand the combine part and why it works!!
http://tiny-code.blogspot.in/2013/07/spoj-1043can-you-answer-these-queries-i.html
can anyone please help me with an example on how to write the combine part?
I am stucked in this problem since the last 2 days.

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