#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, _x[N], _y[N], ps[N], pL[N][N], pR[N][N], pmx[N][N];
void prec() {
for (ll gl = 0; gl < n; gl++) {
for (ll gr = gl; gr < n; gr++) {
vector<ll> a;
for (ll i = gl; i <= gr; i++) a.push_back(y[i]);
sort(a.begin(), a.end());
pL[gl][gr] = a[0];
pR[gl][gr] = r - 1 - a[gr - gl];
for (ll i = 1; i < a.size(); i++) pmx[gl][gr] = max(pmx[gl][gr], a[i] - a[i - 1] - 1);
}
}
}
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]--;
iota(ps, ps + n, 0);
sort(ps, ps + n, [&](ll a, ll b) { return x[a] < x[b]; });
for (ll i = 0; i < n; i++) _x[i] = x[ps[i]], _y[i] = y[ps[i]];
for (ll i = 0; i < n; i++) swap(x[i], _x[i]), swap(y[i], _y[i]);
prec();
for (ll up = 0; up < n; up++) { // n
vll cup;
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]));
}
}
sort(cup.begin(), cup.end());
cup.resize(unique(cup.begin(), cup.end()) - cup.begin());
for (ll dn = 0; dn < cup.size(); dn++) { // n^3
long long mx = 0, L = 0, R = 0;
vector<ll> cp{0, r - 1};
for (ll i = 0; i < n; i++) { // n^4
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(cp.begin(), cp.end());
cp.resize(unique(cp.begin(), cp.end()) - cp.begin());
ll itl = 0, itr = -1;
for (auto p: cp) { // n^4
while (itl < n && x[itl] + cup[dn] < p) itl++;
while (itr + 1 < n && x[itr + 1] - x[up] <= p) itr++;
if (itl > itr) {
mx = 1e18;
break;
}
mx = max(mx, pmx[itl][itr]);
L = max(L, pL[itl][itr]);
R = max(R, pR[itl][itr]);
}
ans = min(ans, max(mx, L + R) + cup[dn] + x[up]);
}
}
cout << ans;
}
