#include <bits/stdc++.h>
using namespace std;

int main() {
    // input
    int n, m, k; cin >> n >> m >> k;
    bool carpet[n+2][m+2];
    for (int i = 0; i <= n+1; i++) {
        for (int j = 0; j <= m+1; j++) {
            carpet[i][j] = true;
        }
    }
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= m; j++) {
            carpet[i][j] = false;
        }
    }
    for (int i = 0; i < k; i++) {
        int x, y; cin >> x >> y;
        carpet[x][y] = true;
    }

    // algorithm
    int ans = min(n, m);

    // rows
    for (int i = 1; i <= n; i++) {
        int prev = 0;
        for (int j = 1; j <= n+1; j++) {
            if (!carpet[i][j]) continue;
            if (j-prev-1 != 0) ans = min(j-prev-1, ans);
            prev = j;
        }
    }
    // cols
    for (int j = 1; j <= n; j++) {
        int prev = 0;
        for (int i = 1; i <= n+1; i++) {
            if (!carpet[i][j]) continue;
            if (i-prev-1 != 0) ans = min(i-prev-1, ans);
            prev = i;
        }
    }

    cout << ans << endl;
}