#define DEBUG 0
#include <bits/stdc++.h>
using namespace std;
#if DEBUG
// basic debugging macros
int __i__,__j__;
#define printLine(l) for(__i__=0;__i__<l;__i__++){cout<<"-";}cout<<endl
#define printLine2(l,c) for(__i__=0;__i__<l;__i__++){cout<<c;}cout<<endl
#define printVar(n) cout<<#n<<": "<<n<<endl
#define printArr(a,l) cout<<#a<<": ";for(__i__=0;__i__<l;__i__++){cout<<a[__i__]<<" ";}cout<<endl
#define print2dArr(a,r,c) cout<<#a<<":\n";for(__i__=0;__i__<r;__i__++){for(__j__=0;__j__<c;__j__++){cout<<a[__i__][__j__]<<" ";}cout<<endl;}
#define print2dArr2(a,r,c,l) cout<<#a<<":\n";for(__i__=0;__i__<r;__i__++){for(__j__=0;__j__<c;__j__++){cout<<setw(l)<<setfill(' ')<<a[__i__][__j__]<<" ";}cout<<endl;}
// advanced debugging class
// debug 1,2,'A',"test";
class _Debug {
public:
template<typename T>
_Debug& operator,(T val) {
cout << val << endl;
return *this;
}
};
#define debug _Debug(),
#else
#define printLine(l)
#define printLine2(l,c)
#define printVar(n)
#define printArr(a,l)
#define print2dArr(a,r,c)
#define print2dArr2(a,r,c,l)
#define debug
#endif
// define
#define MAX_VAL 999999999
#define MAX_VAL_2 999999999999999999LL
#define EPS 1e-6
#define mp make_pair
#define pb push_back
// typedef
typedef unsigned int UI;
typedef long long int LLI;
typedef unsigned long long int ULLI;
typedef unsigned short int US;
typedef pair<int,int> pii;
typedef pair<LLI,LLI> plli;
typedef vector<int> vi;
typedef vector<LLI> vlli;
typedef vector<pii> vpii;
typedef vector<plli> vplli;
// ---------- END OF TEMPLATE ----------
int S[300],E[300];
int main() {
int i;
int R,C,N;
scanf("%d %d %d",&R,&C,&N);
for (i = 0; i < N; i++) scanf("%d %d",&S[i],&E[i]),S[i]--,E[i]--;
int j,k,l,m,n;
LLI ans = 1e10;
if (R <= 40) {
for (int u = 0; u < R; u++) {
for (int d = 0; d < R; d++) {
vector<pair<int,pii> > vv;
for (i = 0; i < N; i++) {
vv.pb(mp(max(S[i]-u,0),mp(-1,E[i])));
vv.pb(mp(min(S[i]+d+1,R),mp(1,E[i])));
}
int l = 0,r = 0,lr = 0;
multiset<int> SS;
sort(vv.begin(),vv.end());
for (i = 0; i < vv.size(); i++) {
if (vv[i].second.first == -1) SS.insert(vv[i].second.second);
else SS.erase(SS.find(vv[i].second.second));
if ((i < vv.size()-1) && (vv[i].first < vv[i+1].first)) {
if (SS.empty()) l = 2e9;
else {
l = max(l,*SS.begin());
r = max(r,C-*SS.rbegin()-1);
for (auto it = SS.begin(); it != SS.end(); it++) {
auto it2 = it;
it2++;
if (it2 != SS.end()) lr = max(lr,*it2-*it-1);
}
}
}
}
if (vv[0].first != 0) l = 2e9;
if (vv.back().first != R) l = 2e9;
if (lr > l+r) r += lr-l-r;
ans = min(ans,(LLI) u+d+l+r);
}
}
}
else {
for (i = 0; i < N; i++) {
for (j = 0; j < N; j++) {
int r = C-E[i]-1,u = S[j];
vi dd;
for (k = 0; k < N; k++) {
for (l = 0; l < N; l++) dd.pb(max(S[k]-S[l]-u-1,0));
dd.pb(R-S[k]-1);
}
dd.pb(0);
dd.resize(unique(dd.begin(),dd.end())-dd.begin());
for (k = 0; k < dd.size(); k++) {
int d = dd[k];
int L = 0;
vi poss;
vector<pair<int,pair<int,pii> > > vv;
poss.pb(0),poss.pb(C);
for (m = 0; m < N; m++) {
poss.pb(E[m]),poss.pb(min(E[m]+r+1,C));
vv.pb(mp(max(S[m]-u,0),mp(-1,mp(E[m],min(E[m]+r+1,C)))));
vv.pb(mp(min(S[m]+d+1,R),mp(1,mp(E[m],min(E[m]+r+1,C)))));
}
sort(poss.begin(),poss.end());
poss.resize(unique(poss.begin(),poss.end())-poss.begin());
int temp[100];
fill(temp,temp+poss.size(),0);
sort(vv.begin(),vv.end());
for (m = 0; m < vv.size(); m++) {
int s = lower_bound(poss.begin(),poss.end(),vv[m].second.second.first)-poss.begin();
int e = lower_bound(poss.begin(),poss.end(),vv[m].second.second.second)-poss.begin();
for (n = s; n < e; n++) temp[n] -= vv[m].second.first;
if ((m < vv.size()-1) && (vv[m].first < vv[m+1].first)) {
int last = 2e9;
for (n = poss.size()-2; n >= 0; n--) {
if (temp[n] > 0) last = poss[n];
else L = max(L,last-poss[n]);
}
}
}
if (vv[0].first != 0) L = 2e9;
if (vv.back().first != R) L = 2e9;
ans = min(ans,(LLI) r+u+L+d);
}
}
}
}
printf("%lld\n",ans);
return 0;
}
