static public double ret_f(int n)
        {
            n++;
            return Math.Round((Math.Pow((Math.Sqrt(5) + 1) / 2,n)-Math.Pow((-Math.Sqrt(5) + 1) / 2,n))/Math.Sqrt(5));
        
        }

        static public void fib()
        {
           
            double ak = a;
            double bk = b;
            double a2, b2,k=-1;
            int n = 1;
            double cur = 1,cur1=1;
            while (Math.Abs((bk - ak)) / e > cur)
            {
                double s = cur;
                cur = cur1 + cur;
                cur1 = s;
                n++;
            }

          

            a2 = ak + (bk - ak) * ret_f(n - 2) / ret_f(n);
            b2 = ak + (bk - ak) * ret_f(n - 1) / ret_f(n);
            do
            {
                k++;
                
                if (Function(fun, a2) > Function(fun, b2))
                { ak = a2; a2 = b2; b2 = ak + (bk - ak) * ret_f(n - 2 - (int)k) / ret_f(n - 1 - (int)k); }
                else { bk = b2; b2 = a2; a2 = ak + (bk - ak) * ret_f(n - 3 - (int)k) / ret_f(n - 1 - (int)k); }

            } while (k!=(n-3));

            double yn1 = b2;
            double zn1 = a2 + l;

            if(Function(fun,yn1)>Function(fun,zn1))
            {
                double r = (ak + zn1) / 2;
                resu = Function(fun, (yn1 + bk) / 2).ToString();
            }
            else
            {
                double r2 = (ak + zn1) / 2;
                resu = Function(fun, (ak + zn1) / 2).ToString();
            }
            
        }