#ifdef DeBuG
#include "debug.h"
#else
#include <bits/stdc++.h>
#define dbg(...)
#endif
using namespace std;
#define fi first
#define se second
#define pb push_back
#define sz(v) (int)(v).size()
#define all(v) begin(v),end(v)
#define rep(i,a,b) for (int i=(a);i<(b);++i)
using ll = long long; template <class T> using V = vector<T>;
using pii = pair<int,int>; using pll = pair<ll,ll>;
int calc (bitset<41> &f, int c) {
int ret = 0;
for (int i = 1; i <= c; ++i) if (f[i] == 0) {
int j = i;
while (j + 1 <= c && f[j + 1] == 0) ++j;
ret = max(ret, j - i + 1);
i = j;
}
return ret;
}
int main() {
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
int r, c, n;
cin >> r >> c >> n;
V<int> x(n), y(n);
for (int i = 0; i < n; ++i) cin >> x[i] >> y[i];
int ans = r + c - 2;
V<bitset<41>> b(41);
for (int i = 0; i < n; ++i) b[x[i]][y[i]] = 1;
for (int u = 0; u < r; ++u) for (int d = 0; d < r; ++d) {
V<bitset<41>> f = b;
for (int i = 0; i < u; ++i) {
for (int j = 1; j < r; ++j) f[j] |= f[j + 1];
}
for (int i = 0; i < d; ++i) {
for (int j = r; j > 1; --j) f[j] |= f[j - 1];
}
bool bad = false;
for (int j = 1; j <= r; ++j) if (f[j] == 0) bad = true;
if (bad) continue;
for (int l = 0; l < c; ++l) {
V<bitset<41>> foo = f;
for (int i = 0; i < l; ++i) for (int j = 1; j <= r; ++j) foo[j] |= foo[j] << 1;
bad = false;
for (int j = 1; j <= r; ++j) if (foo[j][c] == 0) bad = true;
if (bad) continue;
int ri = 0;
for (int j = 1; j <= r; ++j) {
ri = max(ri, calc(foo[j], c));
}
if (u + d + l + ri < ans) {
dbg(u, d, l, ri);
ans = min(ans, u + d + l + ri);
}
}
}
cout << ans << "\n";
return 0;
}
