#include <bits/stdc++.h>
using namespace std;
using pint = pair<int, int>;
#define all(x) x.begin(), x.end()
const int D[]{0, 1, 0, -1};
struct DSU {
int par[200001];
DSU() { memset(par, -1, sizeof par); }
int find(int x) { return par[x] < 0 ? x : par[x] = find(par[x]); }
void merge(int a, int b) {
if ((a = find(a)) == (b = find(b))) return;
if (-par[a] > -par[b]) swap(a, b);
par[b] += par[a];
par[a] = b;
}
};
vector<pint> adj[200001];
int jump[200001][18][2], dep[200001];
void dfs(int i, int p = 0) {
for (auto [j, d]: adj[i]) {
if (j == p) continue;
dep[j] = dep[i] + 1;
jump[j][0][0] = i, jump[j][0][1] = d;
dfs(j, i);
}
}
int main() {
int R, C, p, Q;
cin >> R >> C >> p >> Q;
int seen[R][C];
for (auto &row: seen) {
for (auto &b: row) {
char c;
cin >> c;
b = c == '.' ? 0 : -1;
}
}
queue<pair<pint, int>> q;
for (int i = 1; i <= p; ++i) {
int r, c;
cin >> r >> c;
--r, --c;
q.push({{r, c}, seen[r][c] = i});
}
DSU dsu;
int t[R][C]{};
vector<array<int, 3>> edges;
while (not q.empty()) {
auto [loc, i] = q.front();
auto [r, c] = loc;
q.pop();
for (int j = 4; j--;) {
int r2 = r + D[j], c2 = c + D[j ^ 1];
if (r2 < 0 or r2 >= R or c2 < 0 or c2 >= C) continue;
if (not seen[r2][c2]) {
q.push({{r2, c2}, seen[r2][c2] = i});
t[r2][c2] = t[r][c] + 1;
} else if (~seen[r2][c2] and seen[r2][c2] != i) edges.push_back({t[r2][c2] + t[r][c], seen[r2][c2], i});
}
}
sort(all(edges));
for (auto &[w, u, v]: edges) {
if (dsu.find(u) != dsu.find(v)) {
adj[u].emplace_back(v, w);
adj[v].emplace_back(u, w);
dsu.merge(u, v);
}
}
for (int i = 1; i <= p; ++i) {
if (dsu.find(i) == i) dfs(i);
}
for (int j = 1; j < 18; ++j) {
for (int i = 1; i <= p; ++i) {
jump[i][j][0] = jump[jump[i][j - 1][0]][j - 1][0];
jump[i][j][1] = max(jump[i][j - 1][1], jump[jump[i][j - 1][0]][j - 1][1]);
}
}
while (Q--) {
int i, j;
cin >> i >> j;
if (dsu.find(i) == dsu.find(j)) {
int ans = 0;
if (dep[i] > dep[j]) swap(i, j);
for (int k = 18; k--;) {
if (dep[j] - (1 << k) >= dep[i]) {
ans = max(ans, jump[j][k][1]);
j = jump[j][k][0];
}
}
for (int k = 18; k--;) {
if (jump[i][k][0] != jump[j][k][0]) {
ans = max({ans, jump[i][k][1], jump[j][k][1]});
i = jump[i][k][0];
j = jump[j][k][0];
}
}
if (i != j) ans = max({ans, jump[i][0][1], jump[j][0][1]});
cout << ans << endl;
} else cout << "-1\n";
}
}
