#include <algorithm>
#include <cstdio>
using ll = long long;
std::pair<ll, int> imp[605];
struct motonic_queue
{
int que[605], *arr, he, ta;
motonic_queue(int *_arr) : arr(_arr), he(0), ta(-1) {}
inline void pop(int pos)
{
while (he <= ta && que[he] < pos)
he++;
}
inline void push(int pos)
{
while (he <= ta && arr[imp[pos].second] >= arr[imp[que[ta]].second])
ta--;
que[++ta] = pos;
}
inline ll front() { return arr[imp[que[he]].second]; }
};
struct point { ll x, y; } arr[305];
int idx[305], lp[305], rp[305], H, W, n, cnt;
int sum[200005], A[605], B[605], C[605];
bool vis[605][305];
inline void 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++)
{
y = idx[i];
if (!vis[x][y])
continue;
if (-1 == lst)
A[x] = arr[y].y - 1;
else
B[x] = std::max<int>(B[x], arr[y].y - lst - 1);
lst = arr[y].y;
}
C[x] = W - lst;
}
inline ll solve()
{
motonic_queue que_A(A), que_B(B), que_C(C);
ll ans = W * 2;
for (int i = 0, j = 0; i < n * 2 && imp[i].first + H <= imp[n * 2 - 1].first; i++)
{
que_A.pop(i);
que_B.pop(i);
que_C.pop(i);
while (j < n * 2 && imp[i].first + H > imp[j].first)
{
que_A.push(j);
que_B.push(j);
que_C.push(j);
j++;
}
ans = std::min(ans, std::max(que_A.front() + que_C.front(), que_B.front()));
}
return ans;
}
int main()
{
// freopen("loj-2390.in", "r", stdin);
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; });
sum[cnt++] = arr[0].x - 1 + H - arr[n - 1].x;
for (int i = 1; i < n; i++)
sum[0] = std::max<int>(sum[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 (sum[0] < arr[i].x - arr[j].x - 1 + H)
sum[cnt++] = arr[i].x - arr[j].x - 1 + H;
if (i > j && sum[0] < arr[i].x - arr[j].x - 1)
sum[cnt++] = arr[i].x - arr[j].x - 1;
}
}
std::sort(sum, sum + cnt);
cnt = std::unique(sum, sum + cnt) - sum;
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 i = 0; i < cnt; i++)
{
for (int j = 0; j < n; j++)
{
while (lp[j] < n && arr[j].x + sum[i] >= arr[lp[j]].x)
{
if (arr[j].x <= arr[lp[j]].x)
add(lp[j], j);
lp[j]++;
}
while (rp[j] < n && arr[j].x + sum[i] + 1 >= arr[rp[j]].x)
{
if (arr[j].x < arr[rp[j]].x)
add(j + n, rp[j]);
rp[j]++;
}
imp[j] = {arr[j].x, j};
imp[j + n] = {arr[j].x + sum[i] + 1, j + n};
}
std::merge(imp, imp + n, imp + n, imp + n + n, imp);
ans = std::min(ans, sum[i] + solve());
}
printf("%lld\n", ans);
return 0;
}
