#include "bits/stdc++.h"
using namespace std;
typedef long long ll;
typedef pair<ll, ll> pll;
typedef vector<ll> vll;
const ll N = 305;
ll n, r, c, x[N], y[N], ans = 1e18, x1[N];
signed main() {
ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
cin >> r >> c >> n;
for (ll i = 0; i < n; i++) cin >> x[i] >> y[i], x[i]--, y[i]--;
for (ll up = 0; up < n; up++) {
vll cup;
for (ll i = 0; i < n; i++) x1[i] = max(0ll, x[i] - x[up]);
for (ll i = 0; i < n; i++) {
cup.push_back(r - 1 - x[i]);
for (ll j = i; j < n; j++) {
cup.push_back(max(0ll, abs(x[i] - x[j]) - 1 - x[up]));
}
}
for (ll dn = 0; dn < cup.size(); dn++) {
long long mx = 0, L = 0, R = 0;
vector<ll> cp{0, r - 1};
vector<array<ll, 3>> scan;
for (ll i = 0; i < n; i++) {
scan.push_back({max(0ll, x[i] - x[up]), 1, y[i]});
scan.push_back({min(r, x[i] + cup[dn] + 1), -1, y[i]});
cp.push_back(min(r - 1, max(0ll, x[i] - x[up] + 0)));
cp.push_back(max(0ll, min(r - 1, x[i] + cup[dn] + 1)));
}
sort(scan.begin(), scan.end());
sort(cp.begin(), cp.end());
cp.resize(unique(cp.begin(), cp.end()) - cp.begin());
multiset<ll> s;
s.insert(-1);
s.insert(c);
multiset<ll> q;
q.insert(c);
ll it = 0;
for (auto p: cp) {
while (it < scan.size() && scan[it][0] <= p) {
ll f = scan[it][2];
if (scan[it][1] == 1) {
s.insert(f);
auto i = s.find(f), l = prev(i), r = next(i);
q.erase(q.find(*r - *l - 1));
q.insert(*r - f - 1);
q.insert(f - *l - 1);
} else {
auto i = s.find(f), l = prev(i), r = next(i);
q.insert(*r - *l - 1);
q.erase(q.find(*r - f - 1));
q.erase(q.find(f - *l - 1));
s.erase(s.find(f));
}
it++;
}
if (s.size() == 2) mx = 1e18;
else mx = max(mx, (long long) *--q.end());
L = max(L, (long long) *next(s.begin()));
R = max(R, (long long) c - 1 - *prev(--s.end()));
}
ans = min(ans, max(mx, L + R) + cup[dn] + x[up]);
}
}
cout << ans;
}
