#include <bits/stdc++.h>
using namespace std;

#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;

#include <bits/extc++.h> /// include-line, keep-include

const ll INF = numeric_limits<ll>::max() / 4;

struct MCMF {
	struct edge {
		int from, to, rev;
		ll cap, cost, flow;
	};
	int N;
	vector<vector<edge>> ed;
	vi seen;
	vector<ll> dist, pi;
	vector<edge*> par;

	MCMF(int N) : N(N), ed(N), seen(N), dist(N), pi(N), par(N) {}

	void addEdge(int from, int to, ll cap, ll cost) {
		if (from == to) return;
		ed[from].push_back(edge{ from,to,sz(ed[to]),cap,cost,0 });
		ed[to].push_back(edge{ to,from,sz(ed[from])-1,0,-cost,0 });
	}

	void path(int s) {
		fill(all(seen), 0);
		fill(all(dist), INF);
		dist[s] = 0; ll di;

		__gnu_pbds::priority_queue<pair<ll, int>> q;
		vector<decltype(q)::point_iterator> its(N);
		q.push({ 0, s });

		while (!q.empty()) {
			s = q.top().second; q.pop();
			seen[s] = 1; di = dist[s] + pi[s];
			for (edge& e : ed[s]) if (!seen[e.to]) {
				ll val = di - pi[e.to] + e.cost;
				if (e.cap - e.flow > 0 && val < dist[e.to]) {
					dist[e.to] = val;
					par[e.to] = &e;
					if (its[e.to] == q.end())
						its[e.to] = q.push({ -dist[e.to], e.to });
					else
						q.modify(its[e.to], { -dist[e.to], e.to });
				}
			}
		}
		rep(i,0,N) pi[i] = min(pi[i] + dist[i], INF);
	}

	pair<ll, ll> maxflow(int s, int t) {
		ll totflow = 0, totcost = 0;
		while (path(s), seen[t]) {
			ll c = 0;
			for (edge* x = par[t]; x; x = par[x->from])
				c += x->cost;

			if (c > 0) break;

			ll fl = INF;
			for (edge* x = par[t]; x; x = par[x->from])
				fl = min(fl, x->cap - x->flow);

			totflow += fl;
			for (edge* x = par[t]; x; x = par[x->from]) {
				x->flow += fl;
				ed[x->to][x->rev].flow -= fl;
			}
		}
		rep(i,0,N) for(edge& e : ed[i]) totcost += e.cost * e.flow;
		return {totflow, totcost/2};
	}

	// If some costs can be negative, call this before maxflow:
	void setpi(int s) { // (otherwise, leave this out)
		fill(all(pi), INF); pi[s] = 0;
		int it = N, ch = 1; ll v;
		while (ch-- && it--)
			rep(i,0,N) if (pi[i] != INF)
			  for (edge& e : ed[i]) if (e.cap)
				  if ((v = pi[i] + e.cost) < pi[e.to])
					  pi[e.to] = v, ch = 1;
		assert(it >= 0); // negative cost cycle
	}
};

int main() {
    cin.tie(0)->sync_with_stdio(0);

	const int inf = 1e9;
    int r, c, b, t;
    cin >> c >> r >> b >> t;
    vector<vector<vi>> whomst(r, vector<vi>(c));

    vector<string> grid(r);
    rep(i, 0, r) cin >> grid[i];
    pii goal;
    rep(i, 0, r) rep(j, 0, c) if (grid[i][j] == 'K') goal = pii(i, j);
    vector<pii> targets;
    rep(i, 0, t) {
        int a, b;
        cin >> b >> a;
        a--; b--;
        targets.emplace_back(a, b);
    }
    t++;
    targets.push_back(goal);
    rep(i, 0, t) {
        whomst[targets[i].first][targets[i].second].push_back(i);
    }

    using p3 = tuple<int, int, int>;
    vector<vi> dist(t, vi(t, inf));
    vector<pii> dirs = { {0,1},{0,-1},{1,0},{-1,0} };
    rep(i, 0, t) {
        queue<p3> q;
        q.emplace(0, targets[i].first, targets[i].second);
        vector<vi> vis(r, vi(c));
        while (q.size())
        {
            int d, a, b;
            tie(d, a, b) = q.front();
            q.pop();
            if (vis[a][b]) continue;
            vis[a][b] = 1;
            for (auto w : whomst[a][b]) dist[i][w] = d;

            for (auto dir : dirs) {
                pii np = pii(a + dir.first, b + dir.second);
                if (np.first < 0 || np.second < 0 || np.first >= r || np.second >= c) continue;
                if (grid[np.first][np.second] == '#') continue;
                q.emplace(d + 1, np.first, np.second);
            }
        }
    }
    rep(i, 0, t) {
        if (dist[i][t - 1] == inf) {
            cout << "impossible";
            return 0;
        }
    }
    int nodecnt = (t - 1) * 2 + 3;
    MCMF flow(nodecnt);

    flow.addEdge(nodecnt - 2, nodecnt - 3, b, 0);
    rep(i, 0, t - 1) {
        flow.addEdge(nodecnt - 3, i * 2, inf, dist[t - 1][i]);
    }
    rep(i, 0, t - 1) {
        flow.addEdge(i * 2, i * 2 + 1, 1, -inf);
    }
    rep(i, 0, t - 1) {
        flow.addEdge(i * 2 + 1, nodecnt - 1, inf, dist[i][t - 1]);
    }
    rep(i, 0, t - 1) {
        rep(j, i + 1, t - 1) {
            flow.addEdge(i * 2 + 1, j * 2, inf, dist[i][j]);
        }
    }
    flow.setpi(nodecnt - 2);
    auto [_, cost] = flow.maxflow(nodecnt - 2, nodecnt - 1);
    cout << cost + (ll)(t - 1) * inf;

	return 0;
}