NK-NK+- is equal to (1+2+3+...+201)-(1+2+3 ...+2012) =-2065438.

k = 1k = 1 20 1 1

20 12 20 12*20 1 1

Calculating:-equals-equals 20 1 1. The original formula of this formula is: -20 1 1+2065438+.

20 1 1 20 1 1

Nk should be "∑" symbol.

Hope to adopt, this is the correct answer.