using System;

public class Program

{

    // Function to find nth odd fibonaci number  

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    static int oddFib(int n)  

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    {  

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        n = (3 * n + 1) / 2;  

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        int a = -1, b = 1, c = 0, i;  

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        for (i = 1; i <= n; i++)  

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        {  

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            c = a + b;  

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            a = b;  

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            b = c;  

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        }  

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        return c;  

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    }  

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    // Driver Code  

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    public static void Main (String[] args)  

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    {  

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        int n = Convert.ToInt32(Console.ReadLine());

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        Console.WriteLine(oddFib(n));  

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    }  

} 

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