#include <bits/stdc++.h>
#define ff first
#define ss second
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
const int INF = 1e9 + 10;
const int SZ = 1010;
int V[3][SZ], D[3][SZ], S[3][SZ][SZ];
ll P[SZ];
int main() {
cin.tie(0); ios_base::sync_with_stdio(0);
int r, c, n;
cin >> r >> c >> n;
vector<pii> T;
for (int i = 0; i < n; i++) {
int x, y;
cin >> x >> y;
T.push_back({--x, --y});
}
sort(T.begin(), T.end());
int X[n], Y[n];
for (int i = 0; i < n; i++) {
tie(X[i], Y[i]) = T[i];
}
set<int> K;
for (int i = 0; i < n; i++) {
for (int j = 0; j < n; j++) {
if (X[i] != X[j]) {
K.insert(abs(X[i] - X[j]));
K.insert(abs(X[i] - X[j]) + 1);
}
K.insert(X[i] + r - X[j]);
K.insert(X[j] + r - X[i]);
}
}
for (int i = 0; i < n; i++) {
multiset<int> st;
int mx = 0;
for (int j = i; j < n; j++) {
st.insert(Y[j]);
}
int p = -1;
for (int x : st) {
if (p != -1) {
mx = max(mx, x - p);
}
p = x;
}
for (int j = n - 1; j >= i; j--) {
S[0][i][j] = *st.begin();
S[1][i][j] = c - *prev(st.end());
S[2][i][j] = mx;
auto it = st.find(Y[j]);
if (it != st.begin() && it != prev(st.end())) {
mx = max(mx, *next(it) - *prev(it));
}
st.erase(it);
}
}
auto calc = [&](ll k) {
int sz = 0;
auto f = [&](ll x) {
if (sz == 0 || P[sz - 1] != x) P[sz++] = x;
};
f(0);
int q = 0;
for (int i = 0; i < n; i++) {
while (q < n && X[q] + k < X[i]) f(X[q++] + k);
f(X[i]);
}
while (q < n) f(X[q++] + k);
f(r + k - 1);
int s = 0, e = 0;
for (int i = 1; i < sz; i++) {
while (e < n && X[e] < P[i]) ++e;
while (s < n && X[s] < P[i] - k) ++s;
for (int t = 0; t < 3; t++) {
V[t][i] = s < e ? S[t][s][e - 1] : max(1, t) * INF;
}
}
int ps[3]{}, pe[3]{};
auto push = [&](int j) {
for (int t = 0; t < 3; t++) {
while (pe[t] > ps[t] && V[t][D[t][pe[t] - 1]] <= V[t][j]) {
--pe[t];
}
D[t][pe[t]++] = j;
}
};
auto pop = [&](int j) {
for (int t = 0; t < 3; t++) {
if (pe[t] > ps[t] && D[t][ps[t]] == j) {
++ps[t];
}
}
};
s = 1;
e = 1;
auto get_sum = [&]() {
return max(V[0][D[0][ps[0]]] + V[1][D[1][ps[1]]], V[2][D[2][ps[2]]]);
};
while (e < sz && P[e - 1] < r) push(e++);
int mn = get_sum();
while (true) {
ll ts = P[s];
ll te = P[e - 1] + 1 - r;
if (min(ts, te) >= k) {
break;
}
if (ts < te) {
pop(s++);
}
else if (te < ts) {
push(e++);
}
else {
pop(s++);
push(e++);
}
mn = min(mn, get_sum());
}
return (ll)k - 1 + mn - 1;
};
ll ans = r + c;
for (int k : K) if (k - 1 < ans) ans = min(ans, calc(k));
cout << ans << '\n';
}
