#include <algorithm>
#include <cstdio>
using ll = long long;
struct point { ll x, y; } arr[305];
struct queue
{
int que[605], val[605], he = 0, ta = -1;
ll *arr;
queue(ll *_arr) : arr(_arr) {}
inline void push(int x, int y)
{
while (he <= ta && arr[y] >= arr[val[ta]])
ta--;
que[++ta] = x;
val[ta] = y;
}
inline void pop(int pos)
{
while (he <= ta && que[he] < pos)
he++;
}
inline ll front() const { return arr[val[he]]; }
};
std::pair<ll, int> val[605];
int lp[305], rp[305], idx[305];
ll ava[200005], A[605], B[605], C[605];
bool vis[605][305];
int main()
{
// freopen("JOISC2017-D1T1.in", "r", stdin);
int H, W, n, cnt = 0;
scanf("%d%d%d", &H, &W, &n);
for (int i = 0; i < n; i++)
scanf("%lld%lld", &arr[i].x, &arr[i].y);
std::sort(arr, arr + n, [&] (point a, point b) { return a.x < b.x; });
ava[cnt++] = arr[0].x - 1 + H - arr[n - 1].x;
for (int i = 1; i < n; i++)
ava[0] = std::max(ava[0], arr[i].x - arr[i - 1].x - 1);
for (int i = 0; i < n; i++)
{
for (int j = 0; j < n; j++)
{
if (i == j)
continue;
if (i > j && arr[i].x - arr[j].x - 1 > ava[0])
ava[cnt++] = arr[i].x - arr[j].x - 1;
if (arr[i].x - 1 + H - arr[j].x > ava[0])
ava[cnt++] = arr[i].x - 1 + H - arr[j].x;
}
}
std::sort(ava, ava + cnt);
cnt = std::unique(ava, ava + cnt) - ava;
for (int i = 0; i < n; i++)
idx[i] = i;
std::sort(idx, idx + n, [&] (int x, int y) { return arr[x].y < arr[y].y; });
ll ans = 1e18;
for (int t = 0; t < cnt; t++)
{
auto add = [&] (int x, int y)
{
vis[x][y] = true;
int lst = -1;
A[x] = B[x] = C[x] = 0;
for (int i = 0; i < n; i++)
{
if (!vis[x][idx[i]])
continue;
if (-1 == lst)
A[x] = arr[idx[i]].y - 1;
else
B[x] = std::max(B[x], arr[idx[i]].y - lst - 1);
lst = arr[idx[i]].y;
}
C[x] = W - lst;
};
for (int i = 0; i < n; i++)
{
while (lp[i] < n && arr[i].x + ava[t] >= arr[lp[i]].x)
{
if (arr[i].x <= arr[lp[i]].x)
add(lp[i], i);
lp[i]++;
}
while (rp[i] < n && arr[i].x + ava[t] + 1 >= arr[rp[i]].x)
{
if (arr[i].x < arr[rp[i]].x)
add(i + n, rp[i]);
rp[i]++;
}
val[i] = {arr[i].x, i};
val[i + n] = {arr[i].x + ava[t] + 1, i + n};
}
std::merge(val, val + n, val + n, val + n * 2, val);
queue que[] = {A, B, C};
for (int i = 0, j = 0; i < n * 2 && val[i].first + H <= val[n * 2 - 1].first; i++)
{
for (auto &Q : que)
Q.pop(i);
while (j < n * 2 && val[i].first + H > val[j].first)
{
for (auto &Q : que)
Q.push(j, val[j].second);
j++;
}
ans = std::min(ans, std::max(que[0].front() + que[2].front(), que[1].front()) + ava[t]);
}
}
printf("%lld\n", ans);
return 0;
}
