#include <bits/stdc++.h>
using namespace std;
int h,w,p,qq;
char mp[2005][2005];
int ufds_par[200005];
unordered_set<int> qr_at[200005];
int ans[200005];
int xc[200005], yc[200005];
int colour[2005][2005];
int dist[2005][2005];
int dx[]={-1,1,0,0};
int dy[]={0,0,1,-1};
int root(int x){
if(ufds_par[x] == -1) return x;
return ufds_par[x] = root(ufds_par[x]);
}
void merge(int x, int y, int d){
for(int i : qr_at[y]){
if(qr_at[x].count(i)){
ans[i] = d;
qr_at[x].erase(i);
}
else qr_at[x].insert(i);
}
qr_at[y].clear();
}
void connect(int u, int v, int d){
int x=root(u), y=root(v);
if(x==y) return;
if(qr_at[x].size() > qr_at[y].size()){
merge(x,y,d);
ufds_par[y] = x;
}
else{ merge(y,x,d); ufds_par[x] = y;}
}
int main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL); cout.tie(NULL);
cin>>h>>w>>p>>qq;
for(int i=1; i<=h; i++){
for(int j=1; j<=w; j++){
cin>>mp[i][j];
}
}
for(int i=1; i<=p; i++) cin>>xc[i]>>yc[i];
for(int i=0; i<qq; i++){
int a,b;
cin>>a>>b;
qr_at[a].insert(i); qr_at[b].insert(i);
}//input
memset(ufds_par,-1,sizeof(ufds_par));
//Multi-BFS
queue<pair<int,int> > q;
memset(dist,-1,sizeof(dist));
memset(colour,-1,sizeof(colour));
memset(ans,-1,sizeof(ans));
for(int i=1; i<=p; i++){
dist[xc[i]][yc[i]] = 0;
colour[xc[i]][yc[i]] = i;
q.emplace(xc[i],yc[i]);
}
int ld = 0;
vector<pair<int,pair<int,int> > > edg;
while(!q.empty()){
int x=q.front().first, y=q.front().second;
q.pop();
for(int i=0; i<4; i++){
int nx=x+dx[i],ny=y+dy[i];
if(nx<=0||nx>h||ny<=0||ny>w) continue;
if(mp[nx][ny] == '#') continue;
if(dist[nx][ny]==-1){
dist[nx][ny] = dist[x][y]+1;
colour[nx][ny] = colour[x][y];
q.push(make_pair(nx,ny));
}
else{
//All offline.
if(colour[x][y] == colour[nx][ny]) continue;
edg.push_back(make_pair(dist[x][y]+dist[nx][ny],make_pair(colour[x][y],colour[nx][ny])));
}
}
}
sort(edg.begin(),edg.end());
for(auto i : edg){
int w=i.first, u=i.second.first, v=i.second.second;
if(root(u)==root(v)) continue;
connect(u,v,w);
}
for(int i=0; i<qq; i++){
//assert(ans[i]!=-1);
cout<<ans[i]<<'\n';
}
/*for(int i=1; i<=p; i++){
cout<<root(i);
}*/
}
