/* Author : Mychecksdead */
#include<bits/stdc++.h>
using namespace std;
#define ll long long int
#define MOD (1000000000+7)
#define MOD1 (998244353)
#define pb push_back
#define all(x) x.begin(), x.end()
#define en cout << '\n'
#define ff first
#define ss second
#define pii pair<int,int>
#define vi vector<int>
const int N = 1e6+100, M = 1e5+10, K = 52, MX = 30;
ll n, m, w;
array<ll, 2> a[N];
void solve(){
cin >> n >> m >> w;
vector<array<ll, 2>> ST;
ll mn = n, mx = 1;
for(int i = 1; i <= w; ++i){
cin >> a[i][0] >> a[i][1];
mn = min(mn, a[i][0]);
mx = max(mx, a[i][0]);
}
for(int i = 1; i <= w; ++i){
ST.pb({max(1ll, a[i][0] - (mn - 1)), min(n, a[i][0] + (n - mx))});
}
vector<ll> U, D;
for(auto [l, r]: ST){
U.pb(l - 1);
D.pb(n - r);
for(auto [l2, r2]: ST){
if(r < l2 || r2 < l){
if(r < l2){
D.pb(l2 - r - 1);
U.pb(l2 - r - 1);
}else{
D.pb(l - r2 - 1);
U.pb(l - r2 - 1);
}
}
}
}
sort(all(U));
sort(all(D));
U.erase(unique(all(U)), U.end());
D.erase(unique(all(D)), D.end());
ll ans = 1e18;
for(ll u: U){
u = u + (mn - 1);
for(ll d: D){
d = d + (n - mx);
// cerr << u << ' ' << d << '\n';
vector<array<ll, 3>> A, B;
vector<ll> X;
for(int i = 1; i <= w; ++i){
A.pb({a[i][0] - u, a[i][0] + d, a[i][1]});
B.pb({a[i][0] + d, a[i][0] - u, a[i][1]});
X.pb(a[i][0] - u);
X.pb(a[i][0] + d + 1);
// cerr << A.back()[0] << ' ' << A.back()[1] << ' '<< A.back()[2] << '\n';
}
X.pb(1);
X.pb(n);
sort(all(A));
sort(all(B));
sort(all(X));
X.erase(unique(all(X)), X.end());
int ptr = 0, ptr2 = 0;
ll L = 0, R = 0, D = 0;
multiset<ll> Y; // active columns
for(ll x_pos: X){
if(x_pos < 1 || x_pos > n) continue;
// cerr << l << ' ' << r << ' ' << col << '\n';
while(ptr < B.size() && B[ptr][0] < x_pos){
Y.erase(Y.find(B[ptr][2]));
++ptr;
}
while(ptr2 < A.size() && A[ptr2][0] <= x_pos){
Y.insert(A[ptr2][2]);
++ptr2;
}
if(Y.empty()){
L = INT_MAX - d - u;
R = D = 0;
break;
}
L = max(L, (*Y.begin()) - 1);
R = max(R, m - (*prev(Y.end())));
ll last_val = (*Y.begin());
for(auto val: Y){
D = max(D, val - last_val - 1);
last_val = val;
}
}
// cerr << L << ' ' << R << ' ' << D << ' ' << d << ' ' << u << ' ' << L + R + max(0, D - L - R) + d + u << '\n';
ans = min(ans, L + R + max(0ll, D - L - R) + d + u);
}
}
cout << ans;
}
int main(){
cin.tie(0); ios::sync_with_stdio(0);
int tt = 1, aa;
// freopen("in.txt", "r", stdin);
// freopen("out.txt", "w", stdout);
while(tt--){
solve();
en;
}
cerr<<"time taken : "<<(float)clock()/CLOCKS_PER_SEC<<" seconds\n";
return 0;
}
