#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""
Created on Mon Jun  3 19:26:47 2019

@author: sercangul
"""

n = 5
xy = [map(int, input().split()) for _ in range(n)]
sx, sy, sx2, sxy = map(sum, zip(*[(x, y, x**2, x * y) for x, y in xy]))
b = (n * sxy - sx * sy) / (n * sx2 - sx**2)
a = (sy / n) - b * (sx / n)
print('{:.3f}'.format(a + b * 80))
[]