def get_exp_from_ato(level, ato):
     curr_level_exp = exp_to_level.keys()[level-1] 
     next_level_exp = exp_to_level.keys()[level] 
     exact_exp = next_level_exp - ato
     if exact_exp < curr_level_exp:
         raise ValueError("Ato exp does not match current level.")
     return exact_exp
 def get_min_exp(level):
     return exp_to_level.keys()[level-1]
 def get_ato(exp):
     index = bisect(exp_to_level.keys(), exp)
     return exp_to_level.keys()[index] - exp
 def calculate_level(exp):
     index = bisect(exp_to_level.keys(), exp)
     return exp_to_level.values()[index-1]