int n = 6,x=1,y=1;
for (int i =1; i < n; i++)
{
y= x - y;
x+= y;

}
Console.WriteLine(x);

 public static int fit(int a)
        {
            if (a>2)
            {
                return fit(a - 1) + fit(a - 2);
            }
            else
            {
                return 1;
              
            }
        }