#include <algorithm>
#include <iostream>
#include <vector>
#define SZ(x) ((int) (x).size())
using namespace std;
typedef long long i64;
const int INF = 0x3f3f3f3f;
struct Cell {
int x, y;
Cell() = default;
Cell(int _x, int _y):
x(_x), y(_y) {}
};
int main() {
#ifdef LOCAL_RUN
freopen("task.in", "r", stdin);
freopen("task.out", "w", stdout);
//freopen("task.err", "w", stderr);
#endif // ONLINE_JUDGE
ios::sync_with_stdio(false);
cin.tie(0);
int n, m, k;
cin >> n >> m >> k;
vector<Cell> cells(k);
for (int i = 0; i < k; ++i) {
cin >> cells[i].x >> cells[i].y;
cells[i].x--; cells[i].y--;
}
int64_t ans = 1LL << 62;
for (int lenUp = 0; lenUp <= n; ++lenUp) {
for (int lenDown = 0; lenDown <= n; ++lenDown) {
vector<vector<int>> cols(n);
for (const Cell& c: cells) {
for (int i = 0; i <= lenUp && c.x - i >= 0; ++i) {
cols[c.x - i].push_back(c.y);
}
for (int i = 0; i <= lenDown && c.x + i < n; ++i) {
cols[c.x + i].push_back(c.y);
}
}
bool ok = true;
int lenLeft = 0, lenRight = 0;
for (vector<int>& ccols: cols) {
if (SZ(ccols) == 0) {
ok = false;
break;
}
sort(ccols.begin(), ccols.end());
ccols.erase(unique(ccols.begin(), ccols.end()), ccols.end());
lenLeft = max(lenLeft, ccols.front());
lenRight = max(lenRight, m - 1 - ccols.back());
}
if (!ok) {
continue;
}
int64_t cans = lenUp + lenDown + lenLeft + lenRight;
int add = 0;
for (const vector<int>& ccols: cols) {
for (int i = 1; i < SZ(ccols); ++i) {
add = max(add,
(ccols[i] - lenLeft) - (ccols[i - 1] + lenRight) - 1);
}
}
cans += add;
ans = min(ans, cans);
}
}
cout << ans << '\n';
}
