Buggy python submission (verdict: Time Limit Exceeded):
n,k = map(int, input().split())
square = [[0]*k*2 for _ in range(k*2)]

for i in range(n):
    x, y, c = input().split()
    x = int(x)
    y = int(y)
    if c=='W':
        y += k
    x = x%(k*2)
    y = y%(k*2)
    square[x][y] += 1

class CumulativeSum2d():
    def __init__(self, collection_2d):
        yl = len(collection_2d)
        xl = len(collection_2d[0])
        self.data = [[0] * (xl+1) for _ in range(yl+1)]
        for y in range(1, yl+1):
            for x in range(1, xl+1):
                top_sum         = self.data[y-1][x]
                left_sum        = self.data[y][x-1]
                dup_sum         = self.data[y-1][x-1]
                self.data[y][x] = top_sum + left_sum - dup_sum
                self.data[y][x] += collection_2d[y-1][x-1]

    def query(self, x, y, x1, y1):
        return self.data[y1][x1] - self.data[y-1][x1] - self.data[y1][x-1] + self.data[y-1][x-1]

cs = CumulativeSum2d(square)

"""
xxxxxx
xxxxxx
xxxxxx
xxxxxx
xxxxxx
xxxxxx

oxxxoo
oxxxoo
oxxxoo
xoooxx
xoooxx
xoooxx

0xxxoo
x000xx
x000xx
x000xx
0xxxoo
0xxxoo

xoooxx
oxxxoo
oxxxoo
oxxxoo
xoooxx
xoooxx

1 k  2k
xxxooo
xxxooo
xxxooo
000xxx
000xxx
000xxx

          1xk  2k
         10xxxoo
         yx000xx
         kx000xx
          x000xx
          0xxxoo
        2k0xxxoo

left top position determine everything
"""
ans = 0
# for x in range(1,k*2+1):
#     for y in range(1,k*2+1):
#         sumd = 0
#         ## main area
#         # center_area
#         sumd += cs.query(x, y, min(k*2, x+k-1), min(k*2, y+k-1))
#         if x-k>1:
#             # left_area
#             sumd += cs.query(1, y, x-k-1, min(k*2, y+k-1))
#         if y-k>1:
#             # top_area
#             sumd += cs.query(x, 1, min(k*2, x+k-1), y-k-1)
#         if x>1 and y>1:
#             # left_top_area
#             sumd += cs.query(max(1, x-k), max(1, y-k), x-1, y-1)
#         if x>1 and y-k<1:
#             # left_bottom_area
#             sumd += cs.query(max(1, x-k), y+k, x-1, k*2)
#         if x-k<1 and y>1:
#             # right_top_area
#             sumd += cs.query(x+k, max(1, y-k), k*2, y-1)
#         if x-k<1 and y-k<1:
#             # right_bottom_area
#             sumd += cs.query(x+k, y+k, k*2, k*2)

#         ans = max(sumd, ans)

s = cs.data
for y in range(k, k*2+1):
    for x in range(k, k*2+1):
        d = cs.query(x-k+1, y-k+1, x, y)
        d += s[y-k][x-k]
        d += s[k*2][x-k] - s[y][x-k]
        d += s[y-k][k*2] - s[y-k][x]
        d += cs.query(x+1,y+1,k*2,k*2)
        ans = max(ans, d, n-d)

print(ans , flush=True)


Fixed submission:
n,k = map(int, input().split())
square = [[0]*k*2 for _ in range(k*2)]

for i in range(n):
    x, y, c = input().split()
    x = int(x)
    y = int(y)
    if c=='W':
        y += k
    x = x%(k*2)
    y = y%(k*2)
    square[x][y] += 1

class CumulativeSum2d():
    def __init__(self, collection_2d):
        yl = len(collection_2d)
        xl = len(collection_2d[0])
        self.data = [[0] * (xl+1) for _ in range(yl+1)]
        for y in range(1, yl+1):
            for x in range(1, xl+1):
                top_sum         = self.data[y-1][x]
                left_sum        = self.data[y][x-1]
                dup_sum         = self.data[y-1][x-1]
                self.data[y][x] = top_sum + left_sum - dup_sum
                self.data[y][x] += collection_2d[y-1][x-1]

    def query(self, x, y, x1, y1):
        return self.data[y1][x1] - self.data[y-1][x1] - self.data[y1][x-1] + self.data[y-1][x-1]

cs = CumulativeSum2d(square)

"""
xxxxxx
xxxxxx
xxxxxx
xxxxxx
xxxxxx
xxxxxx

oxxxoo
oxxxoo
oxxxoo
xoooxx
xoooxx
xoooxx

0xxxoo
x000xx
x000xx
x000xx
0xxxoo
0xxxoo

xoooxx
oxxxoo
oxxxoo
oxxxoo
xoooxx
xoooxx

1 k  2k
xxxooo
xxxooo
xxxooo
000xxx
000xxx
000xxx

          1xk  2k
         10xxxoo
         yx000xx
         kx000xx
          x000xx
          0xxxoo
        2k0xxxoo

left top position determine everything
"""
ans = 0
# for x in range(1,k*2+1):
#     for y in range(1,k*2+1):
#         sumd = 0
#         ## main area
#         # center_area
#         sumd += cs.query(x, y, min(k*2, x+k-1), min(k*2, y+k-1))
#         if x-k>1:
#             # left_area
#             sumd += cs.query(1, y, x-k-1, min(k*2, y+k-1))
#         if y-k>1:
#             # top_area
#             sumd += cs.query(x, 1, min(k*2, x+k-1), y-k-1)
#         if x>1 and y>1:
#             # left_top_area
#             sumd += cs.query(max(1, x-k), max(1, y-k), x-1, y-1)
#         if x>1 and y-k<1:
#             # left_bottom_area
#             sumd += cs.query(max(1, x-k), y+k, x-1, k*2)
#         if x-k<1 and y>1:
#             # right_top_area
#             sumd += cs.query(x+k, max(1, y-k), k*2, y-1)
#         if x-k<1 and y-k<1:
#             # right_bottom_area
#             sumd += cs.query(x+k, y+k, k*2, k*2)

#         ans = max(sumd, ans)

s = cs.data
for y in range(k, k*2+1):
    for x in range(k, k*2+1):
        d = cs.query(x-k+1, y-k+1, x, y)
        d += s[y-k][x-k]
        d += s[k*2][x-k] - s[y][x-k]
        d += s[y-k][k*2] - s[y-k][x]
        d += cs.query(x+1,y+1,k*2,k*2)
        ans = max(ans, d, n-d)

print(ans , flush=True)

Buggy python submission (verdict: Time Limit Exceeded):
n,k = map(int, input().split())
square = [[0 for i in range(k*2)] for j in range(k*2)]

for i in range(n):
    x, y, c = input().split()
    x = int(x)
    y = int(y)
    if c=='W':
        y += k
    x = x%(k*2)
    y = y%(k*2)
    square[x][y] += 1

class CumulativeSum2d():
    def __init__(self, collection_2d):
        yl = len(collection_2d)
        xl = len(collection_2d[0])
        self.data = [[0] * (xl+1) for _ in range(yl+1)]
        for y in range(1, yl+1):
            for x in range(1, xl+1):
                top_sum         = self.data[y-1][x]
                left_sum        = self.data[y][x-1]
                dup_sum         = self.data[y-1][x-1]
                self.data[y][x] = top_sum + left_sum - dup_sum
                self.data[y][x] += collection_2d[y-1][x-1]

    def query(self, x, y, x1, y1):
        return self.data[y1][x1] - self.data[y-1][x1] - self.data[y1][x-1] + self.data[y-1][x-1]

cs = CumulativeSum2d(square)

"""
xxxxxx
xxxxxx
xxxxxx
xxxxxx
xxxxxx
xxxxxx

oxxxoo
oxxxoo
oxxxoo
xoooxx
xoooxx
xoooxx

0xxxoo
x000xx
x000xx
x000xx
0xxxoo
0xxxoo

xoooxx
oxxxoo
oxxxoo
oxxxoo
xoooxx
xoooxx

1 k  2k
xxxooo
xxxooo
xxxooo
000xxx
000xxx
000xxx

          1xk  2k
         10xxxoo
         yx000xx
         kx000xx
          x000xx
          0xxxoo
        2k0xxxoo

left top position determine everything
"""
ans = 0
for x in range(1,k*2+1):
    for y in range(1,k*2+1):
        sumd = 0
        # main_area
        sumd += cs.query(x, y, min(k*2, x+k-1), min(k*2, y+k-1))
        """
        """
        if x-k>1:
            # left_area
            sumd += cs.query(1, y, x-k-1, min(k*2, y+k-1))
        if y-k>1:
            # top_area
            sumd += cs.query(x, 1, min(k*2, x+k-1), y-k-1)
        if x>1 and y>1:
            # left_top_area
            sumd += cs.query(max(1, x-k), max(1, y-k), x-1, y-1)
        if x>1 and y-k<1:
            # left_bottom_area
            sumd += cs.query(max(1, x-k), y+k, x-1, k*2)
        if x-k<1 and y>1:
            # right_top_area
            sumd += cs.query(x+k, max(1, y-k), k*2, y-1)
        if x-k<1 and y-k<1:
            # right_bottom_area
            sumd += cs.query(x+k, y+k, k*2, k*2)
        ans = max(sumd, ans)

print(ans , flush=True)


Fixed submission:
n,k = map(int, input().split())
square = [[0]*k*2 for _ in range(k*2)]

for i in range(n):
    x, y, c = input().split()
    x = int(x)
    y = int(y)
    if c=='W':
        y += k
    x = x%(k*2)
    y = y%(k*2)
    square[x][y] += 1

class CumulativeSum2d():
    def __init__(self, collection_2d):
        yl = len(collection_2d)
        xl = len(collection_2d[0])
        self.data = [[0] * (xl+1) for _ in range(yl+1)]
        for y in range(1, yl+1):
            for x in range(1, xl+1):
                top_sum         = self.data[y-1][x]
                left_sum        = self.data[y][x-1]
                dup_sum         = self.data[y-1][x-1]
                self.data[y][x] = top_sum + left_sum - dup_sum
                self.data[y][x] += collection_2d[y-1][x-1]

    def query(self, x, y, x1, y1):
        return self.data[y1][x1] - self.data[y-1][x1] - self.data[y1][x-1] + self.data[y-1][x-1]

cs = CumulativeSum2d(square)

"""
xxxxxx
xxxxxx
xxxxxx
xxxxxx
xxxxxx
xxxxxx

oxxxoo
oxxxoo
oxxxoo
xoooxx
xoooxx
xoooxx

0xxxoo
x000xx
x000xx
x000xx
0xxxoo
0xxxoo

xoooxx
oxxxoo
oxxxoo
oxxxoo
xoooxx
xoooxx

1 k  2k
xxxooo
xxxooo
xxxooo
000xxx
000xxx
000xxx

          1xk  2k
         10xxxoo
         yx000xx
         kx000xx
          x000xx
          0xxxoo
        2k0xxxoo

left top position determine everything
"""
ans = 0
# for x in range(1,k*2+1):
#     for y in range(1,k*2+1):
#         sumd = 0
#         ## main area
#         # center_area
#         sumd += cs.query(x, y, min(k*2, x+k-1), min(k*2, y+k-1))
#         if x-k>1:
#             # left_area
#             sumd += cs.query(1, y, x-k-1, min(k*2, y+k-1))
#         if y-k>1:
#             # top_area
#             sumd += cs.query(x, 1, min(k*2, x+k-1), y-k-1)
#         if x>1 and y>1:
#             # left_top_area
#             sumd += cs.query(max(1, x-k), max(1, y-k), x-1, y-1)
#         if x>1 and y-k<1:
#             # left_bottom_area
#             sumd += cs.query(max(1, x-k), y+k, x-1, k*2)
#         if x-k<1 and y>1:
#             # right_top_area
#             sumd += cs.query(x+k, max(1, y-k), k*2, y-1)
#         if x-k<1 and y-k<1:
#             # right_bottom_area
#             sumd += cs.query(x+k, y+k, k*2, k*2)

#         ans = max(sumd, ans)

s = cs.data
for y in range(k, k*2+1):
    for x in range(k, k*2+1):
        d = cs.query(x-k+1, y-k+1, x, y)
        d += s[y-k][x-k]
        d += s[k*2][x-k] - s[y][x-k]
        d += s[y-k][k*2] - s[y-k][x]
        d += cs.query(x+1,y+1,k*2,k*2)
        ans = max(ans, d, n-d)

print(ans , flush=True)