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int Fibonacci(int n)
{
   if (1 == n)
   {
       return 1;
   }
   if (2 == n)
   {
       return 2;
   }
   return Fibonacci(n-1) + Fibonacci(n-2);
}

int FibonacciIteration (int n)
{
   int a = 1;
   int b = 2;
   if (n == 1)
       return a;
   if (n == 2)
       return b;
   for (int i = 3; i <= n; i++)   
   {
       int now = a + b;
       a = b;
       b = now;
   }
   return b;
}