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 (2.3.3) (judge verdict: Accepted)

n=gets.to_i
s=[nil]
t=[nil]
n.times do |i|
  s[i+1]=[]
  t[i+1]=[]
end
n.times do |i|
  gets.to_i.times do
    x,y=gets.split.map(&:to_i)
    if y==1
      s[x] << i+1
    else
      t[x] << i+1
    end
  end
end
m=0
[1,0].repeated_permutation(n) do |b|
  c=b.count(1)
  if c<=m
    next
  end
  f=true
  n.times do |i|
    if b[i]==1
      t[i+1].each do |tt|
        if b[tt-1]==1
          f=false
          break
        end
      end
    else
      s[i+1].each do |ss|
        if b[ss-1]==1
          f=false
          break
        end
      end
    end
    if !f
      break
    end
  end
  if f
    m=b.count(1)
  end
end
puts m