import math


def drop_dead_intensity(t):
  """Intensity that can be maintained for a given time.
  
  All athletes assumed to exhibit identical behavior. Originally
  based on elite athletes.

  Args:
    t (float): Time to exhaustion in minutes.
  Returns:
    float: maximum sustainable intensity for this time, defined as a
      ratio of max sustainable VO2 to VO2max.
  """
  a1 = 0.2989558
  a2 = 0.1894393
  tau1 = 1 / 0.1932605
  tau2 = 1 / 0.012778
  c = 0.8

  return a1 * math.exp(-t / tau1) + a2 * math.exp(-t / tau2) + c