#include <iostream>
#include <queue>
#include <vector>
#include <map>
using namespace std;

int main() {
    int L, W;
    cin >> L >> W;

    int barok_req;
    cin >> barok_req;

    int n;
    cin >> n;
    vector<pair<int, int>> v;
    vector<vector<bool>> visited(L, vector<bool>(W, false));
    for(int i = 0; i < n; i++) {
        int x, y;
        cin >> x >> y;
        x--; y--;
        v.push_back(make_pair(x, y));
        visited[x][y] = true;
    }

    queue<vector<pair<int, int>>> q;
    q.push(v);

    queue<int> q_mesec;
    q_mesec.push(n);
    q_mesec.push(0);

    int di[] = {-1, 1, 0, 0};
    int dj[] = {0, 0, -1, 1};
    while(!q.empty()) {
        vector<pair<int, int>> c = q.front();
        q.pop();
        int req = q_mesec.front();
        q_mesec.pop();
        int mesec = q_mesec.front();
        q_mesec.pop();
        if(req >= barok_req) {
            cout << mesec << endl;
            return 0;
        }

        vector<pair<int, int>> t;
        for(int i = 0; i < c.size(); i++) {
            for(int k = 0; k < 4; k++) {
                int ti = c[i].first + di[k];
                int tj = c[i].second + dj[k];

                if(ti >= 0 and ti < L and tj >= 0 and tj < W and !visited[ti][tj]) {
                    t.push_back(make_pair(ti, tj));
                    visited[ti][tj] = true;

                }
            }
        }
        q.push(t);
        q_mesec.push(req + t.size());
        q_mesec.push(mesec + 1);

    }

    return 0;
}