Simple Path#2343
A traveler set out on a journey across his homeland, visiting several cities and making brief stops in each. A path is called simple if the traveler does not visit any city more than once.
Write a program to determine whether the given path is simple.
The first line contains an integer — the number of stops on the journey (1 \le N \le 10000). The second line contains integers, representing the cities where the traveler stopped, listed in the order of visits. Each city is identified by an integer from to 10^6.
Print "YES" if the path is simple; otherwise, print "NO".
Example 1