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