#include <bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define pb push_back
#define mp make_pair
typedef pair<int, int> ii;
const int mod = 1e9 + 7;
const int inf = 1e9;
int add(int x, int y) {
return (1ll * x + 1ll * y) % mod;
}
int del(int x, int y) {
return ((1ll * x - 1ll * y) % mod + mod) % mod;
}
int mul(int x, int y) {
return (1ll * x * 1ll * y) % mod;
}
const int M = 2e5 + 5;
const int N = 2e3 + 5;
int h, w, p, g, d[N][N], type[N][N];
char a[N][N];
vector<ii> query[M];
queue<ii> q;
bool check(int x, int y) {
return (1 <= x && x <= h && 1 <= y && y <= w && a[x][y] != '#');
}
int dx[] = {1, 0, -1, 0};
int dy[] = {0, -1, 0, 1};
vector< pair<int, ii> > edge;
int ans[M], pSet[M], sz[M];
vector<int> vec[M];
int findSet(int u) {
if(u == pSet[u]) return u;
else return pSet[u] = findSet(pSet[u]);
}
void unionSet(int lmao, int u, int v) {
//cout << lmao << " " << u << " " << v << "\n";
u = findSet(u), v = findSet(v);
if(u == v) return ;
if(sz[u] > sz[v]) swap(u, v);
for(int i = 0; i < vec[u].size(); i++) {
int id = vec[u][i];
for(int j = 0; j < query[id].size(); j++) {
ii w = query[id][j];
//cout << id << " " << w.fi << " " << w.se << " " << findSet(w.se) << "\n";
if(findSet(w.se) == v)
ans[w.fi] = lmao;
}
vec[v].pb(id);
}
vec[u].clear();
sz[v] += sz[u];
pSet[u] = v;
}
int main() {
cin.tie(0), ios_base::sync_with_stdio(0);
cin >> h >> w >> p >> g;
for(int i = 1; i <= h; i++) {
for(int j = 1; j <= w; j++)
d[i][j] = inf;
}
for(int i = 1; i <= p; i++) {
pSet[i] = i, sz[i] = 1;
vec[i].pb(i);
}
for(int i = 1; i <= h; i++) {
for(int j = 1; j <= w; j++)
cin >> a[i][j];
}
for(int i = 1; i <= p; i++) {
int u, v;
cin >> u >> v;
d[u][v] = 0;
type[u][v] = i;
q.push({u, v});
}
for(int i = 1; i <= g; i++) {
int u, v;
cin >> u >> v;
query[u].pb({i, v});
query[v].pb({i, u});
}
while(!q.empty()) {
ii x = q.front();
q.pop();
for(int i = 0; i < 4; i++) {
ii y = mp(x.fi + dx[i], x.se + dy[i]);
if(!check(y.fi, y.se)) continue;
if(d[y.fi][y.se] == inf) {
d[y.fi][y.se] = d[x.fi][x.se] + 1;
type[y.fi][y.se] = type[x.fi][x.se];
q.push(y);
}
else if(type[x.fi][x.se] != type[y.fi][y.se])
edge.pb({d[y.fi][y.se] + d[x.fi][x.se], {type[x.fi][x.se], type[y.fi][y.se]}});
}
}
sort(edge.begin(), edge.end());
for(int i = 1; i <= g; i++)
ans[i] = -1;
for(int i = 0; i < edge.size(); i++)
unionSet(edge[i].fi, edge[i].se.fi, edge[i].se.se);
for(int i = 1; i <= g; i++)
cout << ans[i] << "\n";
}
