Cycle Detection in Directed Graphs

You are given a directed graph. Your task is to determine whether the graph contains a cycle.

The graph is given as follows:

• The first line contains an integer n representing the number of vertices.
• The second line contains an integer m representing the number of directed edges.
• Each of the next m lines contains two strings u and v, indicating a directed edge from vertex u to vertex v.

If the graph contains a cycle, output True. Otherwise, output False.

Note: A cycle is defined as a path (of one or more edges) starting and ending at the same vertex.

inputFormat

The input is read from standard input (stdin) and is formatted as follows:

• The first line contains an integer n: the number of vertices in the graph.
• The second line contains an integer m: the number of directed edges in the graph.
• Each of the following m lines contains two space-separated strings representing an edge from the first vertex to the second vertex.

outputFormat

Print a single line to standard output (stdout): True if the graph contains a cycle, and False otherwise.

## sample

4
4
A B
A C
B D
C D

False

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