#include <bits/stdc++.h>
//#include "bits_stdc++.h"
#define f first
#define s second
#define mp make_pair
#define pb push_back
#define lb lower_bound
#define ub upper_bound
#define show(x) cerr << #x << " is " << x << endl;
#define show2(x,y) cerr << #x << " is " << x << " " << #y << " is " << y << endl;
#define show3(x,y,z) cerr << #x << " is " << x << " " << #y << " is " << y << " " << #z << " is " << z << endl;
using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<ld, ll> pd;
typedef pair<string, ll> psl;
typedef pair<ll, ll> pi;
typedef pair<ll, pi> pii;
ll h,w,p, question;
vector<string> m;
ll const MAXN = 200005;
ll const s = 2005;
ll dist[s][s];
bool visited[s][s];
ll par[s][s];
ll twok[MAXN][25];
ll max2k[MAXN][25];
ll depth[MAXN];
ll dx[4] = {0, 1, -1, 0};
ll dy[4] = {1, 0, 0, -1};
vector<pi> adj[MAXN];
vector<pii> edges;
bool compare(pii a, pii b)
{
return a.f<b.f;
}
vector<ll> link, siz;
ll find(ll a) {
ll b = a;
if (link[a] != a) {
b = find(link[a]);
}
link[a] = b;
return b;
}
bool same(ll a, ll b)
{
return find(a)==find(b);
}
void unite(ll a, ll b) {
ll p1 = find(a);
ll p2 = find(b);
if (p1 != p2) {
if (siz[p1] > siz[p2]) {
swap(p1, p2);
}
link[p1] = p2;
siz[p2] += siz[p1];
}
}
void dfs(ll p, ll node)
{
for (pi u: adj[node])
{
if (p==u.f) continue;
twok[u.f][0] = node;
max2k[u.f][0] = u.s;
depth[u.f] = depth[node]+1;
dfs(node, u.f);
}
}
void init()
{
for (ll k=1; k<20; k++)
{
for (ll x=0; x<p; ++x)
{
if (twok[x][k-1]==-1) continue;
twok[x][k] = twok[twok[x][k-1]][k-1];
max2k[x][k] = max(max2k[x][k-1], max2k[twok[x][k-1]][k-1]);
//show3(x, k, max2k[x][k]);
}
}
}
ll lca(ll a, ll b)
{
ll ans = 0;
if (depth[a]<depth[b]) swap(a,b);
ll up = depth[a]-depth[b];
for (ll i=0; i<20; ++i)
{
if (up& (1<<i))
{
ans = max(ans, max2k[a][i]);
a=twok[a][i];
}
}
if (a==b) return ans;
for (ll k=19; k>=0; k--)
{
if (twok[a][k]!=twok[b][k])
{
ans = max(ans, max2k[a][k]);
ans = max(ans, max2k[b][k]);
a=twok[a][k]; b = twok[b][k];
}
}
ans = max(ans, max2k[b][0]);
ans = max(ans, max2k[a][0]);
return ans;
}
int main()
{
cin >> h >> w >> p >> question;
m.resize(h);
for (ll i=0; i<h; ++i) cin >> m[i];
queue<pii> q;
for (ll i=0; i<h; ++i) {for (ll j=0; j<w; ++j){ dist[i][j]=LLONG_MAX;par[i][j] = -1;}}
link.resize(p);
siz.assign(p, 1);
for (ll i=0; i<p; ++i)
{
ll x,y;
cin >> x >> y;
--x, --y;
dist[x][y] = 0;
link[i]=i;
par[x][y] = i;
q.push(mp(i, mp(x,y)));
}
// use bfs to find shortest edges between building
while (q.size())
{
ll b = q.front().f, x = q.front().s.f, y = q.front().s.s;
q.pop();
if (visited[x][y]) continue;
visited[x][y] = true;
for (ll k=0; k<4; ++k)
{
ll newx = x+dx[k], newy = y+dy[k];
if (newx<0 || newx>=h || newy<0 || newy>=w || m[newx][newy]=='#') continue;
if (dist[newx][newy]>dist[x][y]+1)
{
dist[newx][newy] = dist[x][y]+1;
par[newx][newy] = b;
q.push(mp(b, mp(newx, newy)));
}
}
}
for (ll x=0; x<h; ++x)
{
for (ll y=0; y<w; ++y)
{
if (m[x][y]=='#') continue;
for (ll k=0; k<=1; ++k)
{
ll newx = x+dx[k], newy = y+dy[k];
if (newx<0 || newx>=h || newy<0 || newy>=w || m[newx][newy]=='#') continue;
if (par[x][y]!=par[newx][newy] && par[x][y]!=-1 && par[newx][newy]!=-1)
{
edges.pb(mp(dist[x][y]+dist[newx][newy]+1, mp(par[x][y], par[newx][newy])));
}
}
}
}
sort(edges.begin(), edges.end(), compare);
// Krushkal's MST algorithm
for (ll i=0; i<edges.size(); ++i)
{
ll from = edges[i].s.f, to = edges[i].s.s, c = edges[i].f;
if (same(from ,to)) continue;
unite(from, to);
adj[from].pb(mp(to, c));
adj[to].pb(mp(from, c));
//show3(from, to, c);
}
// 2k decomp
for (ll k=0; k<20; k++) {for (ll x=0; x<p; ++x) twok[x][k] = -1; }
for (ll i=0; i<p; ++i) {if (depth[i]==0) {dfs(-1,i);}}
init();
//for (ll k=0; k<2; k++) {for (ll x=0; x<p; ++x) {show3(x,k,twok[x][k]);} }
while (question--)
{
ll x,y;
cin >> x >> y;
--x, --y;
if (!same(x, y)) cout << -1 << endl;
else cout << lca(x, y)-1 << endl;
}
return 0;
}
