from math import exp

def f(t):
  return (800*t+200)*exp(-0.5*t) + 30

def recherche():
  a = 1.75
  b = 20
  while b-a > 0.1 :
    m = (a+b)/2
    if f(m) > 35:
      a = m
    else:
      b = m
  return b