## Problem

**Figure 1**. The graphs from the dataset

Given: A positive integer $k \le 20$ and $k$ simple directed graphs
in the edge list format with at most $10^3$ vertices and $3 \cdot 10^3$ edges each.

Return: For each graph, output "1" if the graph is acyclic and "-1" otherwise.

See Figure 1 for visual example from the sample dataset.

## Sample Dataset

3
2 1
1 2
4 4
4 1
1 2
2 3
3 1
4 3
4 3
3 2
2 1

## Sample Output

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