#include <stdio.h>
#define N 300
#define N_ (1 << 9) /* N_ = pow2(ceil(log2(N))) */
#define N2 (N * 2)
#define INF 0x7fffffff
#define LINF 0x3f3f3f3f3f3f3f3fLL
long long min(long long a, long long b) { return a < b ? a : b; }
long long max(long long a, long long b) { return a > b ? a : b; }
unsigned int X = 12345;
int rand_() {
return (X *= 3) >> 1;
}
int xx[N], yy[N], yy_[N], xx_[N2], xx1[N2], n, x_, y_;
int *zz;
void sort(int *ii, int l, int r) {
while (l < r) {
int i = l, j = l, k = r, i_ = ii[l + rand_() % (r - l)], tmp;
while (j < k)
if (zz[ii[j]] == zz[i_])
j++;
else if (zz[ii[j]] < zz[i_]) {
tmp = ii[i], ii[i] = ii[j], ii[j] = tmp;
i++, j++;
} else {
k--;
tmp = ii[j], ii[j] = ii[k], ii[k] = tmp;
}
sort(ii, l, i);
l = k;
}
}
int stl[N_ * 2], str[N_ * 2], stc[N_ * 2], n_;
void pul(int i) {
int l = i << 1, r = l | 1;
stl[i] = min(stl[l], stl[r]);
str[i] = max(str[l], str[r]);
stc[i] = max(stc[l], stc[r]);
if (str[l] != -1 && stl[r] != INF)
stc[i] = max(stc[i], stl[r] - str[l] - 1);
}
int kk[N];
void update(int i, int x) {
kk[i] += x;
if (kk[i] == 0)
stl[n_ + i] = INF, str[n_ + i] = -1, stc[n_ + i] = 0;
else
stl[n_ + i] = yy_[i], str[n_ + i] = yy_[i], stc[n_ + i] = 0;
i += n_;
while (i > 1)
pul(i >>= 1);
}
long long solve(int w) {
static int ii[N2], ll[N2], rr[N2], cc[N2];
int m, h, i, x, l, r, c;
long long ans;
if (w < 0)
return LINF;
for (i = 0; i < n; i++)
xx_[i << 1 | 0] = xx[i], xx_[i << 1 | 1] = xx[i] + w + 1;
for (i = 0; i < n * 2; i++)
ii[i] = i;
zz = xx_, sort(ii, 0, n * 2);
for (i = 0; i < n_ * 2; i++)
stl[i] = INF, str[i] = -1, stc[i] = 0, kk[i] = 0;
m = 0;
ll[m] = INF, rr[m] = -1, cc[m] = INF, xx1[m] = -INF, m++;
for (h = 0; h < n * 2; h++) {
i = ii[h];
if ((i & 1) == 0)
update(yy[i >> 1], 1);
else
update(yy[i >> 1], -1);
if (h + 1 == n * 2 || xx_[ii[h + 1]] != xx_[ii[h]]) {
if (stl[1] == INF)
ll[m] = INF, rr[m] = -1, cc[m] = INF;
else
ll[m] = stl[1], rr[m] = str[1], cc[m] = stc[1];
xx1[m++] = xx_[ii[h]];
}
}
xx1[m] = INF;
ans = LINF;
for (x = 0; x <= w; x++) {
l = -1, r = INF, c = 0;
for (h = 0; h < m; h++) {
if (xx1[h + 1] <= x || x + x_ <= xx1[h])
continue;
l = max(l, ll[h]), r = min(r, rr[h]), c = max(c, cc[h]);
}
if (l != INF && r != -1 && c != INF)
ans = min(ans, w + max(l + y_ - 1 - r, c));
}
return ans;
}
int main() {
static int ii[N];
int h, i, j, y;
long long ans;
scanf("%d%d%d", &x_, &y_, &n);
for (i = 0; i < n; i++)
scanf("%d%d", &xx[i], &yy[i]), xx[i]--, yy[i]--;
for (i = 0; i < n; i++)
ii[i] = i;
zz = yy, sort(ii, 0, n);
n_ = 0;
for (h = 0; h < n; h++) {
i = ii[h], y = yy[i];
if (n_ == 0 || yy_[n_ - 1] != y)
yy_[n_++] = y;
yy[i] = n_ - 1;
}
n_ = 1;
while (n_ < n)
n_ <<= 1;
ans = LINF;
for (i = 0; i < n; i++)
for (j = 0; j < n; j++)
ans = min(ans, min(solve((x_ - 1 - xx[i]) + (xx[j] - 0)), solve(xx[j] - xx[i] - 1)));
printf("%lld\n", ans);
return 0;
}
