Description

Xiao X gives you the first two terms and the number of terms of an arithmetic progression. Please find the sum of all terms of this arithmetic progression.

Arithmetic progression: For an $n$-term sequence $a$, if for any $i \in [1,n)$ it satisfies $a_{i+1} - a_i = d$, where $d$ is a constant, then this sequence is called an arithmetic progression.

Input Format

One line with $3$ integers $a_1, a_2, n$, representing the 1st and 2nd terms of the arithmetic progression and the number of terms.

Constraints:

• $|a_1|,|a_2| \le 10^6$.
• $3 \le n \le 10^6$.

Output Format

One line with one integer, representing the answer.

1 2 3

6

-5 -10 5

-75

Hint

Sample $1$ Explanation

This arithmetic progression is 1 2 3, and the sum of its terms is $6$.

Translated by ChatGPT 5