File Access Delegation

You are given a set of delegation rules that define which employee can delegate file access rights to another employee. Each rule is represented as a triple of strings (sender, receiver, file). Access rights to a particular file can be passed from one employee to another through direct or indirect delegation. Given a list of rules and a query consisting of an employee and a file name, determine whether the queried employee can obtain access to the file through any chain of delegations. Print YES if access is granted and NO otherwise.

Note: The delegation chain is only considered for the specific queried file. There may be cycles in the delegation rules; your solution should avoid infinite loops.

Example: If the rules are:

• Alice delegates to Bob for Report1
• Bob delegates to Charlie for Report1

Then for the query Charlie Report1, the answer is YES.

inputFormat

The input is given via standard input (stdin) and has the following format:

M
sender1 receiver1 file1
sender2 receiver2 file2
... (M lines in total)
query_employee query_file

Where:

• M is an integer representing the number of delegation rules.
• Each of the next M lines contains three strings: the delegator's name, the delegate's name, and the file name.
• The last line contains two strings: the employee to query and the file name.

outputFormat

Output a single line to standard output (stdout): YES if the employee can get access to the file (directly or through a chain of delegations), otherwise print NO.

## sample

1
Alice Bob Report1
Bob Report1

YES