//recursion

func fib(n int) int{

	if n < 2{

		return n

	}else{

		return fib(n-1) + fib(n-2)

	}

}

func fibcore(n int) (int,int){

	if n < 2{

		return 0,n

	}else{

		a,b := fibcore(n-1)

		return b,a+b

	}

}

//tail recursion

func fib2(n int)(int){

	_,b:= fibcore(n)

	return b

}

//iteration

func fib3(max int)(int){

	n:=0

	a,b:=0,1

	for {

		if n < max{

			a,b = b,a+b

			n ++

		}else{

			break

		}

	}

	return b

}