func main()
	var n: int :: cui@inputInt()
	var x: []int :: #[n]int
	var sum: int :: 0
	for i(0, n - 1)
		do x[i] :: cui@inputInt()
		do sum :+ x[i]
	end for
	var ave: float :: sum $ float / n $ float
	
	var diffSquare: []float :: #[n]float
	var diffSquareSum: float :: 0.0
	for i(0, n - 1)
		do diffSquare[i] :: (ave - x[i] $ float).abs() ^ 2.0
		do diffSquareSum :+ diffSquare[i]
	end for
	var aveDiff: float :: (diffSquareSum / n $ float) ^ 0.5
	
	var m: int :: cui@inputInt() - 1
	var ans: float :: 50.0 + (x[m] $ float - ave) * 10.0 / aveDiff
	do cui@print("\{(ans + 100000000.0) $ int - 100000000}\n")
end func