#include <iostream>
#include <algorithm>
#include <vector>
#include <map>
#include <set>
#include <array>
#include <stack>
#include <queue>
#include <random>
#include <numeric>
#include <functional>
#include <chrono>
#include <utility>
#include <iomanip>
#include <assert.h>
using namespace std;
void dbg_out() { cerr << endl; }
template<typename Head, typename... Tail>
void dbg_out(Head H, Tail... T) { cerr << ' ' << H; dbg_out(T...); }
#define dbg(...) cerr << "(" << #__VA_ARGS__ << "):", dbg_out(__VA_ARGS__)
#define rng_init mt19937 rng(chrono::steady_clock::now().time_since_epoch().count())
#define rng_seed(x) mt19937 rng(x)
#define all(x) (x).begin(), (x).end()
#define sz(x) (int) (x).size()
#define int long long
struct Edge {
int u, v, w;
Edge(int u, int v, int w) : u(u), v(v), w(w) {}
bool operator<(const Edge &b) const {
return w < b.w;
}
};
const int MXN = 2100, INF = 1e15, MXP = 4e5 + 5, MXK = 20;
using pii = pair<int, int>;
int H, W, P, Q;
int grid[MXN][MXN], dist[MXN][MXN], bfs_par[MXN][MXN];
bool valid(int i, int j) {
if (i < 1 || i > H || j < 1 || j > W) return false;
if (grid[i][j] < 0) return false;
return true;
}
int par[MXP], cost[MXP], tin[MXP], tout[MXP], binlift[MXK][MXP];
vector<int> g[MXP];
int new_node, timer;
int get(int x) {
if (par[x] == x) return x;
return par[x] = get(par[x]);
}
void add_edge(int u, int v) {
g[u].push_back(v);
g[v].push_back(u);
}
void unite(int x, int y, int w) {
x = get(x), y = get(y);
if (x == y) return;
cost[new_node] = w;
add_edge(x, new_node);
add_edge(y, new_node);
par[x] = new_node;
par[y] = new_node;
new_node++;
}
void dfs(int u, int p) {
tin[u] = timer++;
for (int k = 1; k < MXK; k++)
binlift[k][u] = binlift[k - 1][binlift[k - 1][u]];
for (const auto &v : g[u]) {
if (v == p) continue;
binlift[0][v] = u;
dfs(v, u);
}
tout[u] = timer - 1;
}
bool is_anc(int v, int u) {
return (tin[v] <= tin[u] && tout[v] >= tout[u]);
}
int get_lca(int u, int v) {
if (is_anc(u, v)) return u;
if (is_anc(v, u)) return v;
for (int i = MXK - 1; i >= 0; i--) {
if (is_anc(binlift[i][u], v)) continue;
u = binlift[i][u];
}
return binlift[0][u];
}
void solve() {
cin >> H >> W >> P >> Q;
for (int i = 0; i <= H + 2; i++) {
for (int j = 0; j <= W + 2; j++) {
grid[i][j] = -1;
dist[i][j] = INF;
}
}
for (int i = 1; i <= H; i++) {
for (int j = 1; j <= W; j++) {
char x;
cin >> x;
if (x == '.') grid[i][j] = 0;
}
}
deque<pii> dq;
for (int i = 1; i <= P; i++) {
int x, y;
cin >> x >> y;
grid[x][y] = i;
dq.emplace_back(x, y);
dist[x][y] = 0;
bfs_par[x][y] = i;
}
int pos[4][2] = {{0, -1}, {-1, 0}, {0, 1}, {1, 0}};
vector<Edge> edges;
while (!dq.empty()) {
auto cur = dq.front();
dq.pop_front();
int x = cur.first, y = cur.second;
for (const auto &[dx, dy] : pos) {
int nx = dx + x, ny = dy + y;
if (!valid(nx, ny)) continue;
if (dist[nx][ny] < INF) {
if (bfs_par[x][y] == bfs_par[nx][ny]) continue;
edges.emplace_back(bfs_par[x][y], bfs_par[nx][ny], dist[x][y] + dist[nx][ny]);
} else {
int wt = (grid[nx][ny] == 0);
if (wt == 0) dq.emplace_front(nx, ny);
else dq.emplace_back(nx, ny);
dist[nx][ny] = dist[x][y] + wt;
bfs_par[nx][ny] = bfs_par[x][y];
}
}
}
// for (int i = 1; i <= H; i++) {
// for (int j = 1; j <= W; j++) {
// cout << bfs_par[i][j] << " ";
// }
// cout << "\n";
// }
sort(all(edges));
// for (const auto &[u, v, w] : edges) {
// cout << u << " " << v << " " << w << "\n";
// }
for (int i = 0; i < MXP; i++) {
par[i] = i;
cost[i] = INF;
}
new_node = P + 1;
for (const auto &[u, v, w] : edges) {
unite(u, v, w);
}
for (int i = 1; i < new_node; i++) {
if (get(i) == i) add_edge(i, 0);
}
dfs(0, -1);
// for (int i = 0; i < MXP; i++) {
// for (const auto &v : g[i]) {
// cout << i << " " << v << "\n";
// }
// }
// dbg(get_lca(1, 2));
while (Q--) {
int u, v;
cin >> u >> v;
int lca = get_lca(u, v);
int ans = cost[lca];
cout << (ans < INF ? ans : -1) << "\n";
}
}
signed main() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
int TC = 1;
// cin >> TC;
while (TC--) solve();
}
