#include <bits/stdc++.h>

using namespace std;

ifstream fin("cladire.in");
ofstream fout("cladire.out");

bitset <1004> a[1004];
int b[1004][1004], n, m, lmax;

void Init()
{
    for(int i=1; i<=n; i++)
        a[i] = ~a[i];
}

int main()
{
    int i, j, p, x, y;
    fin >> n >> m;
    fin >> p;
    Init();
    for(i=1; i<=p; i++)
        {
            fin >> x >> y;
            a[x][y] = 0;
        }

    for(i=1; i<=n; i++)
        for(j=1; j<=m; j++)
        if(a[i][j] == 0) b[i][j] = 0;
    else
        {
            b[i][j] = 1 + min({b[i-1][j], b[i-1][j-1], b[i][j-1]});
            lmax = max(lmax, b[i][j]);
        }
    fout << lmax << "\n";


    return 0;
}