#yuki910

n=int(raw_input())
s=raw_input()
res=0
one=nine=0
for c in s:
 if c=='1':
  one+=1
 elif c=='9':
  if one>0:
   res+=1
   one-=1
  else:
   nine+=1
 else:
  res+=1
res+=min(nine/2,one)
res+=max(0,(one-nine/2)/2)
print res