N=int(input())
BC=[0,0,0,0]
for _ in range(N):
    a,b=map(int,input().split())
    if a%8==0:BC[3]+=b
    elif a%4==0:BC[2]+=b
    elif a%2==0:BC[1]+=b
    else:BC[0]+=b
ans=0
ans+=BC[3]
if BC[2]<BC[1]:
    ans+=BC[2]
    BC[1]-=BC[2]
    BC[2]=0
else:
    ans+=BC[1]
    BC[2]-=BC[1]
    BC[1]=0
ans+=BC[1]//3
print(ans)