c,y=map(int,input().split())
l=[10000,5000,2000,1000,500,100]
m=[]

if y<100*c:
  print("can't exchange")
  exit()

for i in l:
  m.append(y//i)
  y%=i
  
if m[-1]>=c:
  print('no exchange')
  exit()
  
print((c-m[-1]-1)//5*5+5+m[-1])