#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int N = 300 + 7;
const int INF = (int) 1e9 + 7;
int dimx, dimy, n;
struct point {
int x;
int y;
};
bool operator < (point a, point b) {
if (a.x != b.x) return a.x < b.x;
return a.y < b.y;
}
point v[N];
struct Event {
int when;
int l, r;
int coef;
};
bool operator < (Event a, Event b) {
if (a.when != b.when) return a.when < b.when;
return a.coef < b.coef;
}
bool ok(int a, int b, int c, int d) {
bool ok1 = 0, ok2 = 0;
vector<Event> events;
for (int i = 1; i <= n; i++) {
int x1 = v[i].x - a, x2 = v[i].x + b;
int y1 = v[i].y - c, y2 = v[i].y + d;
x1 = max(x1, 1);
x2 = min(x2, dimx);
y1 = max(y1, 1);
y2 = min(y2, dimy);
events.push_back({x1, y1, y2, +1});
if (x2 < dimx) {
events.push_back({x2 + 1, y1, y2, -1});
}
ok1 |= (x1 == 1);
ok2 |= (x2 == dimx);
}
sort(events.begin(), events.end());
if (!ok1 || !ok2) {
return 0;
}
vector<pair<int, int>> intervals;
for (int step = 0; step < (int) events.size(); step++) {
auto it = events[step];
int l = it.l, r = it.r + 1;
if (it.coef == 1) {
intervals.push_back({l, r});
} else {
pair<int, int> pr = {l, r};
for (auto &it : intervals) {
if (it == pr) {
swap(it, intervals.back());
}
}
assert(!intervals.empty());
assert(intervals.back() == pr);
intervals.pop_back();
}
if (step + 1 < (int) events.size() && events[step + 1].when == events[step].when) {
continue;
}
sort(intervals.begin(), intervals.end());
bool good = 1;
int last = 1;
for (auto &it : intervals) {
if (it.first > last) {
good = 0;
break;
}
last = max(last, it.second);
}
good &= (last == dimy + 1);
if (!good) {
return 0;
}
}
return 1;
}
vector<int> cover[N];
signed main() {
ios::sync_with_stdio(0); cin.tie(0);
///freopen ("input", "r", stdin);
cin >> dimx >> dimy >> n;
for (int i = 1; i <= n; i++) {
cin >> v[i].x >> v[i].y;
}
if (dimx > 40) {
return 0;
}
int sol = INF;
for (int a = 0; a <= dimx; a++) {
for (int b = 0; a + b <= dimx; b++) { /// fix north, south
for (int i = 1; i <= dimx; i++) {
cover[i].clear();
}
for (int i = 1; i <= n; i++) {
int l = max(1, v[i].x - a), r = min(dimx, v[i].x + b);
for (int j = l; j <= r; j++) {
cover[j].push_back(i);
}
}
bool ok = 1;
for (int i = 1; i <= dimx; i++) {
if (cover[i].empty()) {
ok = 0;
break;
}
}
if (!ok) {
continue;
}
/// now it's a pretty easy task
/// For each row I have some restrictions
int r1 = 0, r2 = 0, rsum = 0;
for (int i = 1; i <= dimx; i++) {
vector<int> pts;
for (auto &j : cover[i]) {
pts.push_back(v[j].y);
}
sort(pts.begin(), pts.end());
r1 = max(r1, pts[0] - 1);
r2 = max(r2, dimy - pts.back());
for (int j = 1; j < (int) pts.size(); j++) {
rsum = max(rsum, pts[j] - pts[j - 1] - 1);
}
}
rsum = max(rsum, r1 + r2);
sol = min(sol, a + b + rsum);
}
}
cout << sol << "\n";
return 0;
/**
int sol = INF;
for (int a = 0; a <= dimx; a++) {
for (int b = 0; b <= dimx; b++) {
for (int c = 0; c <= dimy; c++) {
for (int d = 0; d <= dimy; d++) {
if (a + b + c + d >= sol) continue;
if (ok(a, b, c, d)) {
sol = a + b + c + d;
}
}
}
}
}
cout << sol << "\n";
**/
return 0;
}
