Problem p02922 (python)

Fixed submission:
A, B = map(int, input().split())
i = 1
socket = 0
while i < B:
    i += A - 1
    socket += 1
print(socket)

Buggy submission (verdict: Runtime Error):
import numpy as np
ls = np.array([[ 0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,
         0,  0,  0,  0],
       [ 0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15,
        16, 17, 18, 19],
       [ 0,  1,  1,  2,  2,  3,  3,  4,  4,  5,  5,  6,  6,  7,  7,  8,
         8,  9,  9, 10],
       [ 0,  1,  1,  1,  2,  2,  2,  3,  3,  3,  4,  4,  4,  5,  5,  5,
         6,  6,  6,  7],
       [ 0,  1,  1,  1,  1,  2,  2,  2,  2,  3,  3,  3,  3,  4,  4,  4,
         4,  5,  5,  5],
       [ 0,  1,  1,  1,  1,  1,  2,  2,  2,  2,  2,  3,  3,  3,  3,  3,
         4,  4,  4,  4],
       [ 0,  1,  1,  1,  1,  1,  1,  2,  2,  2,  2,  2,  2,  3,  3,  3,
         3,  3,  3,  4],
       [ 0,  1,  1,  1,  1,  1,  1,  1,  2,  2,  2,  2,  2,  2,  2,  3,
         3,  3,  3,  3],
       [ 0,  1,  1,  1,  1,  1,  1,  1,  1,  2,  2,  2,  2,  2,  2,  2,
         2,  3,  3,  3],
       [ 0,  1,  1,  1,  1,  1,  1,  1,  1,  1,  2,  2,  2,  2,  2,  2,
         2,  2,  2,  3],
       [ 0,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  2,  2,  2,  2,  2,
         2,  2,  2,  2],
       [ 0,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  2,  2,  2,  2,
         2,  2,  2,  2],
       [ 0,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  2,  2,  2,
         2,  2,  2,  2],
       [ 0,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  2,  2,
         2,  2,  2,  2],
       [ 0,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  2,
         2,  2,  2,  2],
       [ 0,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,
         2,  2,  2,  2],
       [ 0,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,
         1,  2,  2,  2],
       [ 0,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,
         1,  1,  2,  2],
       [ 0,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,
         1,  1,  1,  2],
       [ 0,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,
         1,  1,  1,  1]])
A, B = map(int, input().split())
print(ls[A][B])

Buggy submission (verdict: Runtime Error):
import numpy as np
ls = np.array([[ 0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,
         0,  0,  0,  0],
       [ 0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15,
        16, 17, 18, 19],
       [ 0,  1,  1,  2,  2,  3,  3,  4,  4,  5,  5,  6,  6,  7,  7,  8,
         8,  9,  9, 10],
       [ 0,  1,  1,  1,  2,  2,  2,  3,  3,  3,  4,  4,  4,  5,  5,  5,
         6,  6,  6,  7],
       [ 0,  1,  1,  1,  1,  2,  2,  2,  2,  3,  3,  3,  3,  4,  4,  4,
         4,  5,  5,  5],
       [ 0,  1,  1,  1,  1,  1,  2,  2,  2,  2,  2,  3,  3,  3,  3,  3,
         4,  4,  4,  4],
       [ 0,  1,  1,  1,  1,  1,  1,  2,  2,  2,  2,  2,  2,  3,  3,  3,
         3,  3,  3,  4],
       [ 0,  1,  1,  1,  1,  1,  1,  1,  2,  2,  2,  2,  2,  2,  2,  3,
         3,  3,  3,  3],
       [ 0,  1,  1,  1,  1,  1,  1,  1,  1,  2,  2,  2,  2,  2,  2,  2,
         2,  3,  3,  3],
       [ 0,  1,  1,  1,  1,  1,  1,  1,  1,  1,  2,  2,  2,  2,  2,  2,
         2,  2,  2,  3],
       [ 0,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  2,  2,  2,  2,  2,
         2,  2,  2,  2],
       [ 0,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  2,  2,  2,  2,
         2,  2,  2,  2],
       [ 0,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  2,  2,  2,
         2,  2,  2,  2],
       [ 0,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  2,  2,
         2,  2,  2,  2],
       [ 0,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  2,
         2,  2,  2,  2],
       [ 0,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,
         2,  2,  2,  2],
       [ 0,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,
         1,  2,  2,  2],
       [ 0,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,
         1,  1,  2,  2],
       [ 0,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,
         1,  1,  1,  2],
       [ 0,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,
         1,  1,  1,  1]])
A, B = map(int, inupt().split())
print(ls[A][B])