Problem:
Score : 400 points

Problem Statement

Snuke has one biscuit and zero Japanese yen (the currency) in his pocket.
He will perform the following operations exactly K times in total, in the order he likes:

Hit his pocket, which magically increases the number of biscuits by one.

Exchange A biscuits to 1 yen.

Exchange 1 yen to B biscuits.

Find the maximum possible number of biscuits in Snuke's pocket after K operations.

Constraints

1 \leq K,A,B \leq 10^9

K,A and B are integers.

Input

Input is given from Standard Input in the following format:

K A B

Output

Print the maximum possible number of biscuits in Snuke's pocket after K operations.

Sample Input 1

4 2 6

Sample Output 1

7

The number of biscuits in Snuke's pocket after K operations is maximized as follows:

Hit his pocket. Now he has 2 biscuits and 0 yen.

Exchange 2 biscuits to 1 yen. his pocket. Now he has 0 biscuits and 1 yen.

Hit his pocket. Now he has 1 biscuits and 1 yen.

Exchange 1 yen to 6 biscuits. his pocket. Now he has 7 biscuits and 0 yen.

Sample Input 2

7 3 4

Sample Output 2

8

Sample Input 3

314159265 35897932 384626433

Sample Output 3

48518828981938099

Solution in C# (Mono 4.6.2.0) (judge verdict: Wrong Answer)

using System;
using System.Linq;

namespace MinPro2019C
{
    internal class Program
    {
        public static void Main(string[] args)
        {
            long[] KAB = Console.ReadLine().Split(' ').Select(a => long.Parse(a)).ToArray();
            long K = KAB[0];
            long A = KAB[1];
            long B = KAB[2];

            if (B - A < 2)
            {
                Console.WriteLine(1 + K);
                return;
            }

            long ans = 0;
            long lest = K;
            if (lest >= A + 1)
            {
                ans += B;
                lest -= A + 1;
            }

            ans += lest / 2 * (B - A) + lest % 2;
            Console.WriteLine(ans);
        }
    }
}