## Codeforces 546A. Soldier and Bananas Question

## A. Soldier and Bananas

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?

Input

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.

Output

Output one integer — the amount of dollars that the soldier must borrow from his friend. If he doesn’t have to borrow money, output 0.

Examples

##### input:

3 17 4

##### output:

13

## Codeforces 546A Soldier and Bananas solution in C++

#include<iostream> using namespace std; int main() { int w,k,z; long long int n; cin>>k>>n>>w; int sum=0; for(int i=1;i<=w;i++) { sum=sum+i; } int m=sum*k; int out=m-n; if(out<0) { cout<<"0"<<endl; } else{ cout<<out<<endl;} }

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