 x   y  z    k
 1   1  2.0  a
 3   1  2.4  a
 2   2  2.8  a
 2   3  2.0  a
 4   2  2.5  a
 8   3  3.1  b
 8   5  3.0  b
 9   4  3.9  b
 9   6  3.6  b
 9   7  3.6  b
10   6  3.3  b
11   4  7.8  c
12   2  7.4  c
12   3  7.0  c
13   2  7.1  c
13   3  7.9  c
 3   9  5.2  d
 4  10  5.5  d
 4  11  5.6  d
 6  10  5.3  d
 7  11  5.3  d
 8  10  5.9  d
 9   9  5.2  d
11  10  5.4  d

