#include<bits/stdc++.h>
using namespace std;
using ll = long long;
const int N = 303;
int s[N], e[N];
int main() {
cin.tie(nullptr)->sync_with_stdio(false);
int r, c;
cin >> r >> c;
int n;
cin >> n;
for (int i = 1;i <= n;i++) cin >> s[i] >> e[i];
// iterate for all O(n ^ 2)
ll mn = LLONG_MAX;
for (int u = 0;u < r;u++) {
for (int d = 0;d < r;d++) {
bool ch = 1;
int mx = 0;
int dl = 0, dr = 0;
multiset<int> ms;
vector<vector<int>> event(r + 1);
for (int i = 1;i <= n;i++) {
for (int j = max(1, s[i] - u);j <= min(r, s[i] + d);j++)
event[j].push_back(e[i]);
}
for (int i = 1;i <= r;i++) {
sort(event[i].begin(), event[i].end());
event[i].resize(unique(event[i].begin(), event[i].end()) - event[i].begin());
if (event[i].empty()) {
ch = 0;
break;
}
int sz = event[i].size();
for (int j = 0;j < sz - 1;j++) {
mx = max(mx, event[i][j + 1] - event[i][j] - 1);
}
dl = max(dl, event[i][0] - 1);
dr = max(dr, c - event[i][sz - 1]);
}
if (ch) {
mn = min(mn, 0ll + u + d + max(dl + dr, mx));
//cout << u << ' ' << d << ' ' << dl << ' ' << dr << ' ' << mx << '\n';
}
}
}
cout << mn << '\n';
return 0;
}
