#include <bits/stdc++.h>
using namespace std;
#define int long long
#define pi pair<int, int>
#define pii pair<int, pair<int, int> >
#define fi first
#define se second
int n, q, r, c;
priority_queue<pair<pi, pii> , vector<pair<pi, pii> >, greater<pair<pi, pii> > > pq;
int A[2005][2005], dist[2005][2005];
char G[2005][2005];
int par[20][200005], mx[20][200005];
vector<int>v[200005];
vector<pi>adj[200005];
int dep[200005];
int root[200005];
pi haha[200005];
vector<pii>edges;
map<pair<int, int> , int> m;
int getr(int x){
return (root[x] == x ? x : root[x] = getr(root[x]));
}
void merge(int a, int b){
a = getr(a), b = getr(b);
if(a != b)root[b] = a;
}
void dfs(int x, int p, int d){
par[0][x] = p;
dep[x] = d;
for(auto [i, j] : adj[x]){
if(i != p)dfs(i, x, d+1);
else mx[0][x] = j;
}
}
int lca(int u, int v){
if(dep[u] > dep[v])swap(u, v);
int diff = dep[v] - dep[u];
int ans = 0;
for(int i=0;i<19;i++)if(diff >> i & 1)ans = max(ans, mx[i][v]), v = par[i][v];
if(u == v)return ans;
for(int i=18;i>=0;i--){
if(par[i][u] != par[i][v]){
ans = max({ans, mx[i][u], mx[i][v]});
u = par[i][u], v = par[i][v];
}
}
return max({ans, mx[0][u], mx[0][v]});
}
inline int conv(int x, int y){
return (x-1) * c + y;
}
int dx[] = {1, 0, -1, 0}, dy[] = {0, 1, 0, -1};
void solve(){
cin >> r >> c >> n >> q;
for(int i=1;i<=r;i++)for(int j=1;j<=c;j++)cin >> G[i][j], dist[i][j] = 1e9;
queue<pii>qu;
for(int i=1;i<=n;i++){
int x,y;cin >> x >> y;
root[i] = i;
A[x][y] = i;
haha[i] = {x, y};
qu.push({i, {x, y}});
dist[x][y] = 0;
}
while(!qu.empty()){
int x = qu.front().fi, y = qu.front().se.fi, z = qu.front().se.se;
qu.pop();
for(int i=0;i<4;i++){
int y1 = y + dx[i];
int z1 = z + dy[i];
if(y1 < 1 || y1 > r || z1 < 1 || z1 > c)continue;
if(G[y1][z1] == '#')continue;
if(dist[y1][z1] > dist[y][z] + 1)dist[y1][z1] = dist[y][z] + 1, A[y1][z1] = x, qu.push({x, {y1, z1}});
}
}
for(int i=1;i<=r;i++){
for(int j=1;j<=c;j++){
if(G[i][j] == '#')continue;
int x = i ,y = j;
for(int k=0;k<2;k++){
int x1 = x + dx[k], y1 = y + dy[k];
if(x1 < 1 || x1 > r || y1 < 1 || y1 > c)continue;
if(G[x1][y1] == '#')continue;
if(A[x][y] != A[x1][y1] && A[x][y] && A[x1][y1]){
edges.push_back({dist[x][y] + dist[x1][y1] + 1, {A[x][y], A[x1][y1]}});
}
}
}
}
/*
for(int i=1;i<=r;i++){
for(int j=1;j<=c;j++)cout << A[i][j] << " ";
cout << '\n';
}
map<pi, int> :: iterator it;
for(it = m.begin(); it != m.end(); it++){
int x = it->first.fi, y = it->fi.se, z = it->se;
edges.push_back({z, {x, y}});
//cout << x << " " << y << " " << z << '\n';
}
*/
sort(edges.begin(), edges.end());
for(auto i: edges){
int a = i.se.fi, b = i.se.se, w = i.fi;
if(getr(a) == getr(b))continue;
merge(a, b);
adj[a].push_back({b, w});
adj[b].push_back({a, w});
//cout << a << " " << b << " " << w << '\n';
}
for(int i=1;i<=n;i++)if(!dep[i])dfs(i, -1, 1);
for(int i=1;i<19;i++){
for(int j=1;j<=n;j++)par[i][j] = par[i-1][par[i-1][j]], mx[i][j] = max(mx[i-1][j], mx[i-1][par[i-1][j]]);
}
while(q--){
int x,y;cin >> x >> y;
if(getr(x) != getr(y))cout << -1 << '\n';
else cout << lca(x, y) -1 << '\n';
}
}
main(){
ios::sync_with_stdio(0);cin.tie(0);
int t = 1;
//cin >> t;
while(t--){
solve();
}
}
