import times, strutils, sequtils, math, algorithm, tables, sets, lists, intsets
import critbits, future, strformat, deques
template `max=`(x,y) = x = max(x,y)
template `min=`(x,y) = x = min(x,y)
template `mod=`(x,y) = x = x mod y
template scan2 = (scan(), scan())
template scan3 = (scan(), scan())
let read* = iterator: string {.closure.} =
    while true: (for s in stdin.readLine.split: yield s)
proc scan(): int = read().parseInt
proc scanf(): float = read().parseFloat
proc toInt(c:char): int =
    return int(c) - int('0')



proc solve():int=
  var
    n = scan()
    s = read()
    one = 0
    three = s.count('3')
    five = s.count('5')
    seven = s.count('7')
    nine = 0
  # 11:素数
  # 19:素数
  # 91:7の倍数
  # 911:素数かもしれないけど11を除去するのでいい
  for c in s:
    if c == '1':
      one+=1
      if one>=2:
        one-=2
        result+=1
    if c == '9':
      nine+=1
      if one>0:
        one-=1
        nine-=1
        result+=1

    
  return result+three+five+seven
  
echo solve()