Lucky key is 8
6,8,it took 2 times
6,2,1,3,4,8,it took 6 times
6,7,1,3,8,it took 5 times
3,6,7,8,it took 4 times
7,4,3,2,6,8,it took 6 times
6,4,8,it took 3 times
3,2,5,1,4,7,6,8,it took 8 times
2,1,5,4,8,it took 5 times
2,8,it took 2 times
5,8,it took 2 times
2,7,5,8,it took 4 times
7,5,8,it took 3 times
1,5,4,7,8,it took 5 times
7,6,5,8,it took 4 times
8,it took 1 times
8,it took 1 times
5,3,8,it took 3 times
4,2,3,6,5,1,7,8,it took 8 times
1,8,it took 2 times
4,3,2,1,5,6,8,it took 7 times
The average is 4.05