Lucky key is 8
5,1,6,8,it took 4 times
1,8,it took 2 times
7,5,3,2,4,6,8,it took 7 times
3,5,7,6,2,8,it took 6 times
4,7,2,3,8,it took 5 times
5,8,it took 2 times
6,2,5,3,8,it took 5 times
1,8,it took 2 times
8,it took 1 times
7,2,4,3,1,6,5,8,it took 8 times
5,3,4,6,7,1,8,it took 7 times
6,4,3,5,7,2,8,it took 7 times
7,5,1,3,8,it took 5 times
7,3,5,4,1,6,8,it took 7 times
2,5,4,8,it took 4 times
6,3,1,4,8,it took 5 times
3,5,8,it took 3 times
1,2,8,it took 3 times
3,1,6,2,8,it took 5 times
4,6,5,1,8,it took 5 times
The average is 4.65