#include<bits/stdc++.h>
using namespace std;
using ll = long long;
const int N = 303;
int s[N], e[N];
int main() {
cin.tie(nullptr)->sync_with_stdio(false);
int r, c;
cin >> r >> c;
int n;
cin >> n;
for (int i = 1;i <= n;i++) cin >> s[i] >> e[i];
set<int> up, down;
// for (int i = 1;i <= n;i++) {
// up.insert(s[i] - 1);
// down.insert(r - s[i]);
// }
for (int i = 0;i < r;i++) up.insert(i), down.insert(i);
// iterate for all O(n ^ 2)
ll mn = LLONG_MAX;
for (auto& u : up) {
for (auto& d : down) {
bool ch = 1;
int mx = 0;
int dl = 0, dr = 0;
multiset<int> ms;
vector<pair<int, int>> event;
for (int i = 1;i <= n;i++) {
event.push_back({ max(1, s[i] - u), e[i] });
event.push_back({ min(r + 1, s[i] + d + 1), -e[i] });
}
ms.insert(0);
ms.insert(c + 1);
sort(event.begin(), event.end());
int sz = event.size();
for (int i = 0, j;i < sz;i = j) {
if (event[i].first == r + 1) break;
for (j = i;j < sz && event[i].first == event[j].first;j++) {
int v = event[j].second;
if (v < 0) ms.erase(ms.find(-v));
else ms.insert(v);
}
for (auto& v : ms) {
if (v == c + 1) continue;
int r = *(ms.upper_bound(abs(v)));
mx = max(mx, r - v - 1);
}
if ((int)ms.size() == 2) {
ch = 0;
break;
}
int fl = *(ms.upper_bound(0));
int fr = *(--ms.lower_bound(c + 1));
dl = max(dl, fl - 1);
dr = max(dr, c - fr);
}
if (ch) {
mn = min(mn, 0ll + u + d + max(dl + dr, mx));
//cout << u << ' ' << d << ' ' << dl << ' ' << dr << ' ' << mx << '\n';
}
}
}
cout << mn << '\n';
return 0;
}
