N=int(input())
AB=list(tuple(map(int,input().split())) for i in range(N))

c1=0
c2=0
c3=0

for a,b in AB:
    if a%8==0:
        c3+=b
    elif a%4==0:
        c2+=b
    elif a%2==0:
        c1+=b

ans=c3
v=min(c1,c2)
ans+=v; c1-=v; c2-=v;
ans+=c2//2+c1//3
print(ans)