#include <bits/stdc++.h>
using namespace std;
typedef long long lint;
typedef long double llf;
typedef pair<int, int> pi;
const int MAXN = 305;
int n, r, c;
pi a[MAXN];
struct sweep{
int pos, val, mode;
bool operator<(const sweep &s)const{
return pi(pos, -mode) < pi(s.pos, -s.mode);
}
};
lint Do(int i, int j){
vector<sweep> sw;
for(int k=0; k<n; k++){
int le = max(1, a[k].first - i);
int ri = min(r, a[k].first + j);
int v = a[k].second;
sw.push_back({le, v, +1});
sw.push_back({ri + 1, v, -1});
}
vector<int> v = {1, r + 1};
for(int i=0; i<sw.size(); i++){
v.push_back(sw[i].pos);
}
sort(sw.begin(), sw.end());
sort(v.begin(), v.end());
v.resize(unique(v.begin(), v.end()) - v.begin());
multiset<int> s;
int ptr = 0;
int lv = 0, rv = 0, sum = 0;
for(int i=0; i+1<v.size(); i++){
while(ptr < sw.size() && sw[ptr].pos == v[i]){
if(sw[ptr].mode == 1) s.insert(sw[ptr].val);
else s.erase(s.find(sw[ptr].val));
ptr++;
}
if(s.size() == 0) return 1e18;
lv = max(lv, *s.begin() - 1);
rv = max(rv, c - *s.rbegin());
auto it = s.begin();
while(next(it) != s.end()){
auto in = next(it);
sum = max(*in - *it - 1, sum);
it = in;
}
}
return (1ll * max(lv + rv, sum)) + i + j;
}
lint solve(){
lint ans = 1e18;
sort(a, a+n);
vector<int> ev;
for(int i=0; i<n; i++){
ev.push_back(a[i].first - 1);
}
sort(ev.begin(), ev.end());
ev.resize(unique(ev.begin(), ev.end()) - ev.begin());
for(auto &l : ev){
vector<int> v;
for(int j=0; j<n; j++){
for(int k=j; k<n; k++){
if(a[k].first - a[j].first >= l) v.push_back(a[k].first - a[j].first - l);
}
v.push_back(r - a[j].first);
}
sort(v.begin(), v.end());
v.resize(unique(v.begin(), v.end()) - v.begin());
for(auto &j : v){
ans = min(ans, Do(l, j));
}
}
return ans;
}
int main(){
cin >> r >> c >> n;
for(int i=0; i<n; i++){
cin >> a[i].first >> a[i].second;
}
lint ans = solve();
for(int i=0; i<n; i++) a[i].first = r + 1 - a[i].first;
ans = min(ans, solve());
cout << ans << endl;
}
