using System;
public class Program
{
// Function to find nth odd fibonaci number
static int oddFib(int n)
n = (3 * n + 1) / 2;
int a = -1, b = 1, c = 0, i;
for (i = 1; i <= n; i++)
c = a + b;
a = b;
b = c;
}
return c;
// Driver Code
public static void Main (String[] args)
int n = Convert.ToInt32(Console.ReadLine());
Console.WriteLine(oddFib(n));