time limit per test1 second

memory limit per test256 megabytes

inputstandard input

outputstandard output

A soldier wants to buy w bananas in the shop. He has to pay k dollars for the first banana, 2k 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 ≤ 109), 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

【题目链接】:http://codeforces.com/contest/546/problem/A

【题解】



就是w个数的等差数列的求和公式。

然后如果钱够的话输出的是0！！！！

否则输出差的绝对值就好.

细心。



【完整代码】

#include <bits/stdc++.h>

using namespace std;

#define lson l,m,rt<<1

#define rson m+1,r,rt<<1|1

#define LL long long

#define rep1(i,a,b) for (int i = a;i <= b;i++)

#define rep2(i,a,b) for (int i = a;i >= b;i--)

#define mp make_pair

#define pb push_back

#define fi first

#define se second

#define rei(x) scanf("%d",&x)

#define rel(x) scanf("%I64d",&x)

typedef pair<int,int> pii;

typedef pair<LL,LL> pll;

//const int MAXN = x;

const int dx[9] = {0,1,-1,0,0,-1,-1,1,1};

const int dy[9] = {0,0,0,-1,1,-1,1,-1,1};

const double pi = acos(-1.0);

LL k,n,w;

int main()

{

    //freopen("F:\\rush.txt","r",stdin);

    rel(k);rel(n);rel(w);

    LL temp1 = (k + w*k)*w/2;

    LL temp = n-temp1;

    if (temp <0)

        cout << abs(temp)<<endl;

    else

        puts("0");

    return 0;

}