A soldier wants to buy *w* bananas in the shop. He has to pay *k* dollars for the first banana, 2*k* dollars for the second one and so on (in other words, he has to pay *i*·*k* dollars for the *i*-th banana).

He has *n* dollars. How many dollars does he have to borrow from his friend soldier to buy *w* bananas?

The first line contains three positive integers *k*, *n*, *w* (1 ≤ *k*, *w* ≤ 1000, 0 ≤ *n* ≤ 10^{9}), the cost of the first banana, initial number of dollars the soldier has and number of bananas he wants.

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