#include <bits/stdc++.h>
using namespace std;
using ll = int;
#define MAXN (200005)
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
ll H,W,P,Q;
char arr[2005][2005];
ll DIST[2005][2005], visited[2005][2005];
pair<ll,ll> building[MAXN];
ll par[MAXN];
ll find_set(ll x){
if(par[x] == x) return x;
par[x] = find_set(par[x]);
return par[x];
}
bool same_set(ll x,ll y){
return find_set(x) == find_set(y);
}
void merge_set(ll x,ll y){
if(same_set(x,y)) return;
par[find_set(x)] = find_set(y);
}
vector<pair<ll,ll> > v[MAXN];
ll dist[MAXN], depth[MAXN];
ll parent[19][MAXN], maxonlev[19][MAXN];
bool vis[MAXN];
void dfs(ll x,ll nodeparent,ll nodedepth){
vis[x] = 1;
parent[0][x] = nodeparent;
depth[x] = nodedepth;
for(ll i = 0;i < v[x].size();i++){
if(v[x][i].first != nodeparent){
maxonlev[0][v[x][i].first] = v[x][i].second;
dfs(v[x][i].first,x,nodedepth + 1);
}
}
}
void lcainit(){
for(ll i = 1;i < 19;i++){
for(ll j = 0;j < P;j++){
parent[i][j] = parent[i - 1][parent[i - 1][j]];
maxonlev[i][j] = max(maxonlev[i - 1][j],maxonlev[i - 1][parent[i - 1][j]]);
}
}
}
ll lca(ll u,ll v){
ll ans = 0;
if(depth[u] > depth[v]){
swap(u,v);
}
ll diff = depth[v] - depth[u];
for(ll i = 0;i < 19;i++){
if(diff & (1<<i)){
ans = max(ans,maxonlev[i][v]);
v = parent[i][v];
}
}
if(u == v){
return ans;
}
for(ll i = 18;i >= 0;i--){
if(parent[i][u] != parent[i][v]){
ans = max(ans,maxonlev[i][u]);
ans = max(ans,maxonlev[i][v]);
u = parent[i][u];
v = parent[i][v];
}
}
ans = max(ans,maxonlev[0][u]);
ans = max(ans,maxonlev[0][v]);
return ans;
}
int main() {
ios_base::sync_with_stdio(false);cin.tie(0);
cin>>H>>W>>P>>Q;
for(ll i = 0;i < H;i++){
for(ll j = 0;j < W;j++){
cin>>arr[i][j];
}
}
queue<pair<pair<ll,ll>,ll> > q; //x, y, source
memset(visited,-1,sizeof(visited));
for(ll i = 0;i < P;i++){
cin>>building[i].first>>building[i].second;
building[i].first--;
building[i].second--;
q.push({{building[i].first,building[i].second},i});
DIST[building[i].first][building[i].second] = 0;
visited[building[i].first][building[i].second] = i;
}
int Hy[] = {0,0,-1,1};
int Wx[] = {-1,1,0,0};
while(!q.empty()){
ll y = q.front().first.first;
ll x = q.front().first.second;
ll source = q.front().second;
q.pop();
visited[y][x] = source;
for(ll i = 0;i < 4;i++){
ll a = y + Hy[i];
ll b = x + Wx[i];
if(a < 0 || a >= H || b < 0 || b >= W || arr[a][b] == '#' || visited[a][b] != -1){
continue;
}
q.push({{a,b},source});
DIST[a][b] = DIST[y][x] + 1;
visited[a][b] = source;
}
}
for(ll i = 0;i < P;i++){
par[i] = i;
}
vector<pair<ll,pair<ll,ll> > > edges;
for(ll y = 0;y < H;y++){
for(ll x = 0;x < W;x++){
if(arr[y][x] == '#' || visited[y][x] == -1) continue;
for(ll i = 0;i < 4;i++){
ll a = y + Hy[i];
ll b = x + Wx[i];
if(a < 0 || a >= H || b < 0 || b >= W || arr[a][b] == '#' || visited[a][b] == -1){
continue;
}
if(visited[y][x] != visited[a][b]){
edges.push_back({DIST[y][x] + DIST[a][b],{visited[y][x],visited[a][b]}});
}
}
}
}
sort(edges.begin(),edges.end());
for(auto u : edges){
ll a = u.second.first;
ll b = u.second.second;
ll c = u.first;
if(same_set(a,b)) continue;
merge_set(a,b);
v[a].push_back({b,c});
v[b].push_back({a,c});
}
for(ll x = 0;x < P;x++){
if(!vis[x]){
dfs(x,0,0);
}
}
lcainit();
for(ll q = 0;q < Q;q++){
ll a,b;
cin>>a>>b;
a--, b--;
if(!same_set(a,b)){
cout<<-1<<'\n';
}else{
cout<<lca(a,b)<<'\n';
}
}
}
