Problems

# Sponsor’s money

# Sponsor’s money

Prize’s Fund of sponsor "I will give you more money than **2** preceding sponsors together" said new sponsor after **2** tournaments in which sponsor spent in S UAN for every tournament. The words like it said every next sponsor.

You know a sum **S**, which give first sponsor, a number of regular tournament N and a sum of scoring in bank what have a sponsor, or that sum which he want to take in debt for prizes.

**Input**

In the first line we have **3** numbers **S**, **N**, **B**. **S** ≤ **1000**, **0** < **N** ≤ **1000**, **B** ≤ **10 ^{300}**.

**Output**

One number is the sum which remains in scoring of sponsor or that sum which he want to take in debt.

Input example #1

3 4 20

Output example #1

9