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문제

It is Saturday and Ann Britt-Caroline is going to buy candy. She has identified several different bags of candy she is considering buying.

Each bag contains a number of pieces of candy of different types. There are 10 types of normal candy (these are numbered $1...10$), and 10 types of anti-candy (numbered $-1...-10$). It just so happens that candy of type $n$ and type $-n$ do not go well together - they are annihilated if they come in contact with each other. Other than that anti-candy tastes just the same as normal candy.

When Ann Britt-Caroline has bought the bags of candy she mixes them in a big bowl such that all pairs of candy/anti-candy is annihilated (she mixes thoroughly). How many pieces of candy can Ann Britt-Caroline have left (after all pairs of candy/ant-candy is annihilated), if she selects her bags of candy optimally? Note that she can only buy one bag of each type. Ignore any money related issues - her parents will pay.

입력

The first line in the input consist of an integer $1 \le N \le 1000$ - the number of bags of candy.

The following $n$ lines describe each bag of candy. Each line starts with an integer $1 \le k \le 10$, specifying the number of different types of candy in the bag. Then follow $k$ pairs of integers $s$ $n$, which means that there are $n$ pieces of candy type $s$. Each type of candy is mentioned at most once per bag, and types $s$ and $-s$ can not be in the same bag.

For all $n$, $1 \le n \le 1000$.

출력

Print an integer: the largest amount of candy Ann Britt-Caroline can have in the end.

제한

• $N \le 1000$

예제 입력 1

3
1 1 3
2 -1 1 -2 5
2 2 2 -3 1


예제 출력 1

7


출처

• 문제를 만든 사람: Simon Lindholm