#include <bits/stdc++.h>
using namespace std;
template<typename A, typename B> ostream& operator<<(ostream &os, const pair<A, B> &p) { return os << '(' << p.first << ", " << p.second << ')'; }
template<typename T_container, typename T = typename enable_if<!is_same<T_container, string>::value, typename T_container::value_type>::type> ostream& operator<<(ostream &os, const T_container &v) { os << '{'; string sep; for (const T &x : v) os << sep << x, sep = ", "; return os << '}'; }
#define ll long long
#define ld long double
#define all(a) (a).begin(), (a).end()
#define sui cout.tie(NULL); cin.tie(NULL); ios_base::sync_with_stdio(false)
const ll MAX_N = 1e5 + 5;
const ll MOD = 1e9 + 7;
const ll INF = 2e9;
const ld EPS = 1e-9;
const ll LOG = 30;
void solve() {
ll r, c;
cin >> r >> c;
vector<pair<ll, ll>> al;
ll n;
cin >> n;
for (ll i = 0; i < n; i++)
{
ll x, y;
cin >> x >> y;
x--, y--;
al.push_back({x, y});
}
ll ans = INF;
for (ll i = 0; i <= r; i++)
{
for (ll j = 0; j <= r; j++)
{
ll cnt0 = 0;
ll cnt1 = 0;
ll cnt2 = 0;
for (ll p = 0; p < r; p++)
{
vector<ll> al1;
for (ll pp = 0; pp < n; pp++)
{
if (al[pp].first <= p)
{
if (al[pp].first >= p - i) al1.push_back(al[pp].second);
} else
{
if (al[pp].first <= p + j) al1.push_back(al[pp].second);
}
}
if (al1.empty()) cnt0 = INF;
else
{
sort(all(al1));
cnt1 = max(cnt1, al1[0]);
cnt2 = max(cnt2, c - 1 - al1.back());
for (ll pp = 0; pp < al1.size() - 1; pp++) cnt0 = max(cnt0, al1[pp + 1] - al1[pp] - 1);
}
}
ans = min(ans, i + j + max(cnt0, cnt1 + cnt2));
}
}
cout << ans << "\n";
}
int main() {
sui;
ll tc = 1;
//cin >> tc;
for (ll t = 1; t <= tc; t++) {
solve();
}
}
