#include <stdio.h>
#include <string.h>
#define N 300
#define N_ (1 << 9) /* N_ = pow2(ceil(log2(N))) */
#define N2 (N * 2 + 5)
#define INF 0x3f3f3f3f
#define LINF 0x3f3f3f3f3f3f3f3fLL
int min(int a, int b) { return a < b ? a : b; }
int max(int a, int b) { return a > b ? a : b; }
long long min_(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], ii[N], ii_[N], n, x_, y_; long long xx_[N2];
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 (xx[ii[j]] == xx[i_])
j++;
else if (xx[ii[j]] < xx[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 lll[N][N], rrr[N][N], ccc[N][N];
long long solve(long long w) {
static int ii_[N2], ll[N2], rr[N2], cc[N2], qul[N2], qur[N2], quc[N2];
static long long xx1[N2];
int m, h, h_, i, il, ir, j, k, l, r, c, headl, cntl, headr, cntr, headc, cntc, 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;
i = 0, j = 0, k = 0;
while (i < n || j < n)
ii_[k++] = j == n || i < n && xx[ii[i]] < xx[ii[j]] + w + 1 ? ii[i++] << 1 | 0 : ii[j++] << 1 | 1;
m = 0;
ll[m] = INF, rr[m] = -1, cc[m] = INF, xx1[m] = -LINF, m++;
for (h = 0, il = ir = 0; h < n * 2; h++) {
i = ii_[h];
if ((i & 1) == 0)
ir++;
else
il++;
if (h + 1 == n * 2 || xx_[ii_[h + 1]] != xx_[ii_[h]]) {
if (il == ir)
ll[m] = INF, rr[m] = -1, cc[m] = INF;
else
ll[m] = lll[il][ir - 1], rr[m] = rrr[il][ir - 1], cc[m] = ccc[il][ir - 1];
xx1[m++] = xx_[ii_[h]];
}
}
xx1[m] = LINF;
ans = INF;
l = -1, r = INF, c = 0;
for (h = 0; h < m; h++) {
if (xx1[h + 1] <= 0 || 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, max(l + y_ - 1 - r, c));
l = -1, r = INF, c = 0;
for (h = 0; h < m; h++) {
if (xx1[h + 1] <= w || w + 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, max(l + y_ - 1 - r, c));
headl = cntl = 0, headr = cntr = 0, headc = cntc = 0;
for (h = 0, h_ = 0; h < m; h++) {
while (h_ < m && xx1[h_] < xx1[h] + x_) {
while (cntl && ll[qul[headl + cntl - 1]] <= ll[h_])
cntl--;
qul[headl + cntl++] = h_;
while (cntr && rr[qur[headr + cntr - 1]] >= rr[h_])
cntr--;
qur[headr + cntr++] = h_;
while (cntc && cc[quc[headc + cntc - 1]] <= cc[h_])
cntc--;
quc[headc + cntc++] = h_;
h_++;
}
if (xx1[h] >= 0 && xx1[h] <= w) {
l = ll[qul[headl]], r = rr[qur[headr]], c = cc[quc[headc]];
if (l != INF && r != -1 && c != INF)
ans = min(ans, max(l + y_ - 1 - r, c));
}
if (qul[headl] == h)
headl++, cntl--;
if (qur[headr] == h)
headr++, cntr--;
if (quc[headc] == h)
headc++, cntc--;
}
return ans == INF ? LINF : ans + w;
}
int main() {
int k, h, i, j, tmp;
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;
sort(ii, 0, n);
for (i = 0; i < n; i++) {
k = 0;
for (j = i; j < n; j++) {
ii_[k++] = ii[j];
for (h = k - 1; h > 0 && yy[ii_[h]] < yy[ii_[h - 1]]; h--)
tmp = ii_[h], ii_[h] = ii_[h - 1], ii_[h - 1] = tmp;
lll[i][j] = yy[ii_[0]];
rrr[i][j] = yy[ii_[k - 1]];
for (h = 1; h < k; h++)
ccc[i][j] = max(ccc[i][j], yy[ii_[h]] - yy[ii_[h - 1]] - 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;
}
