N=int(input())
S=input()

ANS=0

REST=[]

for x in S:
    if x in {"3","5","7"}:
        ANS+=1
    else:
        REST.append(x)

ONE=0
NINE=0
LEN=len(REST)
count19=0

while True:
    while ONE<LEN and REST[ONE]!="1":
        ONE+=1

    NINE=max(ONE,NINE)

    while NINE<LEN and REST[NINE]!="9":
        NINE+=1

    if ONE==LEN or NINE==LEN:
        break
    else:
        count19+=1
        ONE+=1
        NINE+=1


count1=REST.count("1")
ANS+=count19+(count1-count19)//2
print(ANS)