Lucky key is 8
1,4,8,it took 3 times
6,5,8,it took 3 times
7,6,5,3,1,4,2,8,it took 8 times
4,6,1,7,2,3,5,8,it took 8 times
8,it took 1 times
5,6,1,4,2,7,8,it took 7 times
5,1,4,2,6,3,7,8,it took 8 times
5,4,1,2,7,8,it took 6 times
2,5,4,1,3,6,7,8,it took 8 times
7,4,2,5,8,it took 5 times
1,8,it took 2 times
1,8,it took 2 times
4,8,it took 2 times
8,it took 1 times
2,8,it took 2 times
3,8,it took 2 times
5,7,8,it took 3 times
3,5,8,it took 3 times
1,5,6,7,3,4,2,8,it took 8 times
2,7,1,4,3,5,8,it took 7 times
The average is 4.45