import std.stdio, std.conv, std.functional, std.string;
import std.algorithm, std.array, std.container, std.range, std.typecons;
import std.bigint, std.numeric, std.math, std.random;
import core.bitop;

string FMT_F = "%.10f";

static File _f;
void file_io(string fn) { _f = File(fn, "r"); }
static string[] s_rd;
T _RD(T = long)() { while(!s_rd.length) s_rd = readln.chomp.split; string res = s_rd[0]; s_rd.popFront; return res.to!T; }
T _RD(T = long)(File f) { while(!s_rd.length) s_rd = f.readln.chomp.split; string res = s_rd[0]; s_rd.popFront; return res.to!T; }
T[] _RDA(T = long)(T fix = 0) { auto r = readln.chomp.split.to!(T[]); r[] += fix; return r; }
T[] _RDA(T = long)(File f, T fix = 0) { auto r = f.readln.chomp.split.to!(T[]); r[] += fix; return r; }
T RD(T = long)() { if (_f.isOpen) return _RD!T(_f); else return _RD!T; }
T[] RDA(T = long)(T fix = 0) { if (_f.isOpen)  return _RDA!T(_f, fix); else return _RDA!T(fix); }

size_t[] MAKE_IDX(alias less = "a < b", Range)(Range range) { auto idx = new size_t[](range.length); makeIndex!(less)(range, idx); return idx;}
size_t MIN_POS(alias less = "a < b", Range)(Range range) { auto r = minPos!(less)(range); return range.length - r.length; }

void chmin(T)(ref T x, T y) { x = min(x, y); } void chmax(T)(ref T x, T y) { x = max(x, y); }
bool inside(T)(T x, T b, T e) { return x >= b && x < e; }
T lcm(T)(T x, T y) { return x * (y / gcd(x, y)); }
double[] rotate(double[] vec, double rad) { return [cos(rad)*vec[0] - sin(rad)*vec[1], sin(rad)*vec[0] + cos(rad)*vec[1]]; }

long mod = 10^^9 + 7;
//long mod = 998_244_353;
//long mod = 1_000_003;
void moda(ref long x, long y) { x = (x + y) % mod; }
void mods(ref long x, long y) { x = ((x + mod) - (y % mod)) % mod; }
void modm(ref long x, long y) { x = (x * y) % mod; }
void modpow(ref long x, long y) { if (!y) { x = 1; return; } auto t = x; x.modpow(y>>1); x.modm(x); if (y&1) x.modm(t); }
void modd(ref long x, long y) { y.modpow(mod - 2); x.modm(y); }

void main()
{
	auto N = RD;
	auto M = RD;
	auto Q = RD;
	auto a = new long[](Q);
	auto b = new long[](Q);
	auto edges_a = new long[][](N);
	auto edges_b = new long[][](M);
	foreach (i; 0..Q)
	{
		a[i] = RD-1;
		b[i] = RD-1;
		edges_a[a[i]] ~= b[i];
		edges_b[b[i]] ~= a[i];
	}
	/*
	foreach (i; 0..N)
		edges_a[i].sort;
	foreach (i; 0..M)
		edges_b[i].sort;
	*/

	long[] q = [0];
	auto cnt = new long[](10L^^6);
	while (!q.empty)
	{
		auto nd = q.front; q.popFront;
		auto x = nd / (10^^3);
		auto y = nd % (10^^3);
		foreach (i; x..N)
		{
			if (edges_a[i].empty) continue;
			foreach (e; edges_a[i])
			{
				if (e < y) continue;
				auto num = (i+1) * (10^^3) + e+1;
				if (cnt[num] < cnt[nd]+1)
				{
					cnt[num] = cnt[nd]+1;
					q ~= num;
				}
			}
			break;
		}
		foreach (i; y..M)
		{
			if (edges_b[i].empty) continue;
			foreach (e; edges_b[i])
			{
				if (e < x) continue;
				auto num = (e+1) * (10^^3) + i+1;
				if (cnt[num] < cnt[nd]+1)
				{
					cnt[num] = cnt[nd]+1;
					q ~= num;
				}
			}
			break;
		}
	}

	writeln(cnt.maxElement);
	stdout.flush;
	debug readln;
}