Problem:
Score : 300 points

Problem Statement

There are N people numbered 1 to N. Each of them is either an honest person whose testimonies are always correct or an unkind person whose testimonies may be correct or not.

Person i gives A_i testimonies. The j-th testimony by Person i is represented by two integers x_{ij} and y_{ij}. If y_{ij} = 1, the testimony says Person x_{ij} is honest; if y_{ij} = 0, it says Person x_{ij} is unkind.

How many honest persons can be among those N people at most?

Constraints

All values in input are integers.

1 \leq N \leq 15

0 \leq A_i \leq N - 1

1 \leq x_{ij} \leq N

x_{ij} \neq i

x_{ij_1} \neq x_{ij_2} (j_1 \neq j_2)

y_{ij} = 0, 1

Input

Input is given from Standard Input in the following format:

N
A_1
x_{11} y_{11}
x_{12} y_{12}
:
x_{1A_1} y_{1A_1}
A_2
x_{21} y_{21}
x_{22} y_{22}
:
x_{2A_2} y_{2A_2}
:
A_N
x_{N1} y_{N1}
x_{N2} y_{N2}
:
x_{NA_N} y_{NA_N}

Output

Print the maximum possible number of honest persons among the N people.

Sample Input 1

3
1
2 1
1
1 1
1
2 0

Sample Output 1

2

If Person 1 and Person 2 are honest and Person 3 is unkind, we have two honest persons without inconsistencies, which is the maximum possible number of honest persons.

Sample Input 2

3
2
2 1
3 0
2
3 1
1 0
2
1 1
2 0

Sample Output 2

0

Assuming that one or more of them are honest immediately leads to a contradiction.

Sample Input 3

2
1
2 0
1
1 0

Sample Output 3

1

Solution in PyPy3 (2.4.0) (judge verdict: Accepted)

N=int(input())
people=[]
test=[]
for i in range(N):
    a=int(input())
    bufs=[list(map(int,input().split())) for _ in range(a)]
    test.append(bufs)
#print(test)
num=0
for i in range(pow(2,N)):
    flag=1
    flag2=1
    truthtable=[0]*N
    honestunkind=[-1]*N
    for j in range(N):
        if (i>>j)&1:
            truthtable[j]=1
    #print(truthtable)#正直者なら0,嘘つきなら1のtable
    for j in range(N):
        if truthtable[j]==0:
            for k in test[j]:
                people=k[0]-1
                horu=k[1]
                if honestunkind[people]==-1:
                    honestunkind[people]=(horu+truthtable[j]+1)%2
                else:
                    if honestunkind[people]!=(horu+truthtable[j]+1)%2:
                        flag=0
                        break
            if flag==0:
                break
    if flag==1:
        for j in range(N):
            if (truthtable[j]!=honestunkind[j])and(honestunkind[j]!=-1):
                flag2=0
                break
        if flag2==1:
            #print(truthtable,honestunkind)
            num=max(num,truthtable.count(0))
        #print(num,truthtable)
print(num)