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

ANS=0

REST=[]

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

USE=[0]*len(REST)

flag=-1

for i in range(len(REST)):
    if flag==-1:
        if REST[i]=="1":
            flag=i

    else:
        if REST[i]=="9":
            USE[i]=1
            USE[flag]=1
            flag=-1
            ANS+=1

REST2=[]
for i in range(len(REST)):
    if USE[i]==0:
        REST2.append(REST[i])

REST=REST2

USE=[0]*len(REST)

flag=-1

for i in range(len(REST)):
    if flag==-1:
        if REST[i]=="1":
            flag=i

    else:
        if REST[i]=="1":
            USE[i]=1
            USE[flag]=1
            flag=-1
            ANS+=1

REST2=[]
for i in range(len(REST)):
    if USE[i]==0:
        REST2.append(REST[i])

REST=REST2

flag=-1
flag2=-1

for i in range(len(REST)):
    if flag==-1:
        if REST[i]=="9":
            flag=i

    else:
        if flag2==-1:
            if REST[i]=="9":
                flag2=i

        else:
            if REST[i]=="1":
                ANS+=1
                flag=-1
                flag2=-1

print(ANS)