제출 #16355

7 6 6
1 2
1 4
1 7
2 3
2 4
2 5

런타임 에러 (RTE)
stderr:
 Unhandled exception. System.Collections.Generic.KeyNotFoundException: The given key '6' was not present in the dictionary.
   at System.Collections.Generic.Dictionary`2.get_Item(TKey key)
   at Program.<Main>$(String[] args) in /tmp/target/CsharpApp/Program.cs:line 27

6 
6