# Book solution codeforces 743

You are given a book with nn chapters.

Each chapter has a specified list of other chapters that need to be understood in order to understand this chapter. To understand a chapter, you must read it after you understand every chapter on its required list.

Currently you don’t understand any of the chapters. You are going to read the book from the beginning till the end repeatedly until you understand the whole book. Note that if you read a chapter at a moment when you don’t understand some of the required chapters, you don’t understand this chapter.

Determine how many times you will read the book to understand every chapter, or determine that you will never understand every chapter no matter how many times you read the book.

Book solution codeforces

Each test contains multiple test cases. The first line contains the number of test cases tt (1t21041≤t≤2⋅104).

The first line of each test case contains a single integer nn (1n21051≤n≤2⋅105) — number of chapters.

Then nn lines follow. The ii-th line begins with an integer kiki (0kin10≤ki≤n−1) — number of chapters required to understand the ii-th chapter. Then kiki integers ai,1,ai,2,,ai,kiai,1,ai,2,…,ai,ki (1ai,jn,ai,ji,ai,jai,l1≤ai,j≤n,ai,j≠i,ai,j≠ai,l for jlj≠l) follow — the chapters required to understand the ii-th chapter.

It is guaranteed that the sum of nn and sum of kiki over all testcases do not exceed 21052⋅105.

Book solution codeforces

For each test case, if the entire book can be understood, print how many times you will read it, otherwise print 1−1.

Example
input

Copy
5
4
1 2
0
2 1 4
1 2
5
1 5
1 1
1 2
1 3
1 4
5
0
0
2 1 2
1 2
2 2 1
4
2 2 3
0
0
2 3 2
5
1 2
1 3
1 4
1 5
0

Book solution codeforces

Copy
2
-1
1
2
5

Note

In the first example, we will understand chapters {2,4}{2,4} in the first reading and chapters {1,3}{1,3} in the second reading of the book.

In the second example, every chapter requires the understanding of some other chapter, so it is impossible to understand the book.

In the third example, every chapter requires only chapters that appear earlier in the book, so we can understand everything in one go.

In the fourth example, we will understand chapters {2,3,4}{2,3,4} in the first reading and chapter 11 in the second reading of the book.

In the fifth example, we will understand one chapter in every reading from 55 to 11.