Buggy python submission (verdict: Time Limit Exceeded):
import sys
INF = 1 << 60
MOD = 10**9 + 7 # 998244353
sys.setrecursionlimit(2147483647)
input = lambda:sys.stdin.readline().rstrip()
from collections import deque
def resolve():
    m, n, k = map(int, input().split())
    si, sj, ti, tj = map(lambda x : int(x) - 1, input().split())
    grid = [input() for _ in range(m)]

    dist = [[INF] * n for _ in range(m)]
    dist[si][sj] = 0
    D = [(-1, 0), (1, 0), (0, -1), (0, 1)]
    queue = [(si, sj)]
    while queue:
        i, j = queue.pop()
        for di, dj in D:
            for s in range(1, k + 1):
                ni, nj = i + s * di, j + s * dj
                if not (0 <= ni < m and 0 <= nj < n):
                    break
                if grid[ni][nj] == '@':
                    break
                if dist[ni][nj] <= dist[i][j]:
                    break
                if dist[ni][nj] > dist[i][j] + 1:
                    dist[ni][nj] = dist[i][j] + 1
                    queue.append((ni, nj))

    ans = dist[ti][tj]
    if ans == INF:
        ans = -1
    print(ans)
resolve()

Fixed submission:
import sys
INF = 1 << 60
MOD = 10**9 + 7 # 998244353
sys.setrecursionlimit(2147483647)
input = lambda:sys.stdin.readline().rstrip()
from collections import deque
def resolve():
    m, n, k = map(int, input().split())
    si, sj, ti, tj = map(lambda x : int(x) - 1, input().split())
    grid = [input() for _ in range(m)]

    dist = [[INF] * n for _ in range(m)]
    dist[si][sj] = 0
    D = [(-1, 0), (1, 0), (0, -1), (0, 1)]
    queue = deque([(si, sj)])
    while queue:
        i, j = queue.popleft()
        for di, dj in D:
            for s in range(1, k + 1):
                ni, nj = i + s * di, j + s * dj
                if not (0 <= ni < m and 0 <= nj < n):
                    break
                if grid[ni][nj] == '@':
                    break
                if dist[ni][nj] <= dist[i][j]:
                    break
                if dist[ni][nj] > dist[i][j] + 1:
                    dist[ni][nj] = dist[i][j] + 1
                    queue.append((ni, nj))

    ans = dist[ti][tj]
    if ans == INF:
        ans = -1
    print(ans)
resolve()

Buggy python submission (verdict: Time Limit Exceeded):
import sys
INF = 1 << 60
MOD = 10**9 + 7 # 998244353
sys.setrecursionlimit(2147483647)
input = lambda:sys.stdin.readline().rstrip()
from collections import deque
def resolve():
    m, n, k = map(int, input().split())
    si, sj, ti, tj = map(lambda x : int(x) - 1, input().split())
    grid = [input() for _ in range(m)]

    dist = [[INF] * n for _ in range(m)]
    dist[si][sj] = 0
    D = [(-1, 0), (1, 0), (0, -1), (0, 1)]
    queue = [(si, sj)]
    while queue:
        i, j = queue.pop()
        for di, dj in D:
            for s in range(1, k + 1):
                ni, nj = i + s * di, j + s * dj
                if not (0 <= ni < m and 0 <= nj < n):
                    break
                if grid[ni][nj] == '@':
                    break
                if dist[ni][nj] <= dist[i][j]:
                    break
                dist[ni][nj] = dist[i][j] + 1
                queue.append((ni, nj))

    ans = dist[ti][tj]
    if ans == INF:
        ans = -1
    print(ans)
resolve()

Fixed submission:
import sys
INF = 1 << 60
MOD = 10**9 + 7 # 998244353
sys.setrecursionlimit(2147483647)
input = lambda:sys.stdin.readline().rstrip()
from collections import deque
def resolve():
    m, n, k = map(int, input().split())
    si, sj, ti, tj = map(lambda x : int(x) - 1, input().split())
    grid = [input() for _ in range(m)]

    dist = [[INF] * n for _ in range(m)]
    dist[si][sj] = 0
    D = [(-1, 0), (1, 0), (0, -1), (0, 1)]
    queue = deque([(si, sj)])
    while queue:
        i, j = queue.popleft()
        for di, dj in D:
            for s in range(1, k + 1):
                ni, nj = i + s * di, j + s * dj
                if not (0 <= ni < m and 0 <= nj < n):
                    break
                if grid[ni][nj] == '@':
                    break
                if dist[ni][nj] <= dist[i][j]:
                    break
                if dist[ni][nj] > dist[i][j] + 1:
                    dist[ni][nj] = dist[i][j] + 1
                    queue.append((ni, nj))

    ans = dist[ti][tj]
    if ans == INF:
        ans = -1
    print(ans)
resolve()

Buggy python submission (verdict: Time Limit Exceeded):
import sys
INF = 1 << 60
MOD = 10**9 + 7 # 998244353
sys.setrecursionlimit(2147483647)
input = lambda:sys.stdin.readline().rstrip()
from heapq import heappop, heappush
def resolve():
    m, n, k = map(int, input().split())
    si, sj, ti, tj = map(lambda x : int(x) - 1, input().split())
    grid = [input() for _ in range(m)]
    dist = [[[(INF, 0)] * 4 for _ in range(n)] for _ in range(m)]
    heap = []
    for i in range(4):
        dist[si][sj][i] = (0, 0)
        heappush(heap, (0, 0, si, sj, i))

    D = [(-1, 0), (1, 0), (0, -1), (0, 1)]
    while heap:
        d, r, i, j, dir = heappop(heap)
        if dist[i][j][dir] != (d, r):
            continue
        # change direction
        for ndir in range(4):
            nd = (d + (r > 0), 0)
            if dist[i][j][ndir] > nd:
                dist[i][j][ndir] = nd
                heappush(heap, (nd[0], nd[1], i, j, ndir))
        # move to forth
        di, dj = D[dir]
        ni, nj = i + di, j + dj
        if not (0 <= ni < m and 0 <= nj < n):
            continue
        if grid[ni][nj] == '@':
            continue
        nd = (d + 1, 0) if r == k - 1 else (d, r + 1)
        if dist[ni][nj][dir] > nd:
            dist[ni][nj][dir] = nd
            heappush(heap, (nd[0], nd[1], ni, nj, dir))

    ans = INF
    for dir in range(4):
        d, r = dist[ti][tj][dir]
        ans = min(ans, d + (r > 0))
    if ans == INF:
        ans = -1
    print(ans)
resolve()

Fixed submission:
import sys
INF = 1 << 60
MOD = 10**9 + 7 # 998244353
sys.setrecursionlimit(2147483647)
input = lambda:sys.stdin.readline().rstrip()
from collections import deque
def resolve():
    m, n, k = map(int, input().split())
    si, sj, ti, tj = map(lambda x : int(x) - 1, input().split())
    grid = [input() for _ in range(m)]

    dist = [[INF] * n for _ in range(m)]
    dist[si][sj] = 0
    D = [(-1, 0), (1, 0), (0, -1), (0, 1)]
    queue = deque([(si, sj)])
    while queue:
        i, j = queue.popleft()
        for di, dj in D:
            for s in range(1, k + 1):
                ni, nj = i + s * di, j + s * dj
                if not (0 <= ni < m and 0 <= nj < n):
                    break
                if grid[ni][nj] == '@':
                    break
                if dist[ni][nj] <= dist[i][j]:
                    break
                if dist[ni][nj] > dist[i][j] + 1:
                    dist[ni][nj] = dist[i][j] + 1
                    queue.append((ni, nj))

    ans = dist[ti][tj]
    if ans == INF:
        ans = -1
    print(ans)
resolve()