def leastProb(particles):
    '''particles is a dictionary with particle names as keys and probabilities as values.
       Return the particle that is the least probable'''
    leastval = 2
    for p in particles:
        print("Testing particle",p)
        print("lastval so far is",leastval,"particles[p] is",particles[p])
        if particles[p] < leastval:
            leastval = particles[p]
            leastname = p
            print("=> updated leastval to",leastval)
            print("=> updated leastname to",leastname)
    return leastname

def main():
  # The probabilities of detecting certain types of subatonic particles
  particles = {'neutron':0.55,'proton':0.21,'meson':0.03,'muon':0.07,'neutrino':0.14}

  print("the least probable particle is",leastProb(particles))

main()