X,Y=map(int,input().split())
c=[1,5,10,50,100,500,1000,2000,5000,10000]
d={v:i for i,v in enumerate(z)}
a=[0]*len(c)
for v in c[::-1]:
  a[d[v]]=Y//v
  Y%=v
if a[d[100]]>=X:
  print("no exchange")
elif sum(a[d[500]:])>0:
  print(a[d[100]]+5)
else:
  print("can't exchange")