text: from stat_funcs import pcc, stddev, mean
  
  
  def main():
      from sys import stdin
      n = 5
      x, y = [], []
      for line in stdin:
          try:
              a, b = line.strip().split()
          except:
              break
          x.append(int(a))
          y.append(int(b))
      x_given = 80
      print("{:.3f}".format(predict_single(x_given, x, y)))
  
  # def predict(mat1, )
  
  from sklearn import linear_model
  
  def coef_b(xlist, ylist):
      """
      Calculates the b linear regression coefficient
      assuming that \hat y = a + b * xlist
      :param xlist:
      :param ylist:
      :return:
      """
      return pcc(xlist, ylist) * stddev(ylist) / stddev(xlist)
  
  
  def coef_a(xlist, ylist):
      """
      Calculates the a linear regression coefficient
      assuming that \hat y = a + b * xlist
      :param xlist:
      :param ylist:
      :return:
      """
      return mean(ylist) - coef_b(xlist, ylist) * mean(xlist)
  
  
  def predict_single(x_given, xlist, ylist):
      return coef_a(xlist, ylist) + coef_b(xlist, ylist) * x_given
  
  
  if __name__ == "__main__":
      main()
  
  
  