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 Ruby (2.7.1) (judge verdict: Runtime Error)

N = gets.to_i
A = Array.new(20)
x = Array.new(20).map {Array.new(20)}
y = Array.new(20).map {Array.new(20)}

1.upto(N) do |i|
  A[i] = gets.to_i
  1.upto(A[i]) do |j|
    x[i][j], y[i][j] = gets.strip.split.map(&:to_i)
  end
end

ans = 0

[0, 1].repeated_permutation(N) do |persons|
  not_exist = false
  persons.each.with_index(1) do |witness ,i|
    break if not_exist == true
    next if witness == 0
    1.upto(A[i]) do |j|
       match = y[i][j] == bits[x[i][j]-1]
       break not_exist = true if match
    end
  end
  ans = [ans, persons.count(1)].max if not_exist != true
end

print ans.to_i