#include <bits/stdc++.h>
using namespace std;

int h, w, k, xa, ya, xb, yb;
set<int> row[1000005], col[1000005];
vector<pair<int, int>> visited;
vector<vector<int>> dist, dp1, dp2;
vector<string> grid;

int main() {
    // ios_base::sync_with_stdio(false);
    // cin.tie(0);
    // cout.tie(0);
    
    cin >> h >> w >> k >> xa >> ya >> xb >> yb;
    xa--; ya--;
    xb--; yb--;
    grid.resize(h+5);
    dist.assign(h+5, vector<int>(w+5, -1));
    dp1.assign(h+5, vector<int>(w+5, 0));
    dp2.assign(h+5, vector<int>(w+5, 0));
    for (int i = 0; i < h; i++) {
        cin >> grid[i];
        for (int j = 0; j < w; j++) {
            if (grid[i][j] == '.') {
                row[i].insert(j);
                col[j].insert(i);
            }
        }
    }

    for (int i = 0; i < h; i++) {
        for (int j = 0; j < w; j++) {
            if (j) {
                dp1[i][j] = dp1[i][j-1];
            }

            if (grid[i][j] == '@') {
                dp1[i][j]++;
            }
        }
    }

    for (int j = 0; j < w; j++) {
        for (int i = 0; i < h; i++) {
            if (i) {
                dp2[i][j] = dp2[i-1][j];
            }

            if (grid[i][j] == '@') {
                dp2[i][j]++;
            }
        }
    }

    queue<pair<int, int>> q;
    q.push({xa, ya});
    dist[xa][ya] = 0;
    row[xa].erase(ya);
    col[ya].erase(xa);

    while (!q.empty() && dist[xb][yb] == -1) {
        pair<int, int> u = q.front();
        q.pop();

        // left
        auto p = row[u.first].lower_bound(u.second);
        if (p != row[u.first].begin()) {
            p--;
            for (auto it = p; *it >= u.second - k; it--) {
                int res = dp1[u.first][u.second] - (*it == 0 ? 0 : dp1[u.first][*it-1]);
                if (res != 0) {
                    break;
                }

                dist[u.first][*it] = dist[u.first][u.second] + 1;
                q.push({u.first, *it});
                visited.push_back({u.first, *it});

                if (it == row[u.first].begin()) {
                    break;
                }
            }
        }

        // right
        p = row[u.first].lower_bound(u.second);
        for (auto it = p; it != row[u.first].end() && *it <= u.second + k; it++) {
            int res = dp1[u.first][*it] - (u.second == 0 ? 0 : dp1[u.first][u.second-1]);
            if (res != 0) {
                break;
            }

            dist[u.first][*it] = dist[u.first][u.second] + 1;
            q.push({u.first, *it});
            visited.push_back({u.first, *it});
        }

        // up
        p = col[u.second].lower_bound(u.first);
        if (p != col[u.second].begin()) {
            p--;

            for (auto it = p; *it >= u.first - k; it--) {
                int res = dp2[u.first][u.second] - (*it == 0 ? 0 : dp2[*it-1][u.second]);
                if (res != 0) {
                    break;
                }

                dist[*it][u.second] = dist[u.first][u.second] + 1;
                q.push({*it, u.second});
                visited.push_back({*it, u.second});

                if (it == col[u.second].begin()) {
                    break;
                }
            }
        }

        // down
        p = col[u.second].lower_bound(u.first);
        for (auto it = p; it != col[u.second].end() && *it <= u.first + k; it++) {
            int res = dp2[*it][u.second] - (u.first == 0 ? 0 : dp2[u.first-1][u.second]);
            if (res != 0) {
                break;
            }

            dist[*it][u.second] = dist[u.first][u.second] + 1;
            q.push({*it, u.second});
            visited.push_back({*it, u.second});
        }


        for (int i = 0; i < visited.size(); i++) {
            pair<int, int> v = visited[i];
            row[v.first].erase(v.second);
            col[v.second].erase(v.first);
        }
        visited.clear();
    }

    cout << dist[xb][yb] << '\n';

    return 0;
}

Measured memory_bytes: 262476