How many games are in the Half-Life series?
2
2
4
5
2
3
4
5
2
3
4
5
2
3
4
5
2
3
4
5
2
3
4
5
2
3
4
5
2
3
4
5
6
2
3
4
5
6
2
3
7
4
5
6
2
1
3
7
4
5
6
2
1
3
7
4
5
6
2
1
3
7
4
5
6
2
1
3
7
4
5
6
2
1
3
7
4
0
5
6
2
1
3
7
4
5
6
2
8
1
3
0
7
4
5
6
2
8
1
3
7
0
4
5
6
2
8
1
3
7
4
9
0
5
6
2
8
1
3
7
4
9
5
6
8
1
3
10
7
9
6
8
1
10
7
9
6
8
1
10
7
9
6
8
1
10
7
9
6
8
1
10
7
9
6
8
1
10
7
9
6
8
ten
1
10
7
9
6
8
1
13
10
7
ten
9
14
8
1
13
10
7
9
ten
14
8
1
13
25
10
9
14
8
ten
13
25
10
9
17
14
8
13