#include <bits/stdc++.h>

using namespace std;

#define FOR(i, a, b) for(int i = (a); i < (b); i++)
#define RFOR(i, a, b) for(int i = (a) - 1; i >= (b); i--)
#define SZ(a) int(a.size())
#define ALL(a) a.begin(), a.end()
#define PB push_back
#define MP make_pair
#define F first
#define S second

typedef long long LL;
typedef vector<int> VI;
typedef pair<int, int> PII;
typedef double db;

const int N = 1047;

int a[N][N];
int heads[2][N * N];
int sz[2];
int p[N * N];
PII c[N * N];
int n;
int mid;
int r;

void add(int x, int t)
{
	heads[t][sz[t]++] = x;
}

void erase(int pos, int t)
{
	sz[t]--;
	swap(heads[t][pos], heads[t][sz[t]]);
}

PII next(int i)
{
	auto [x, y] = c[i];
	if (x == mid)
		return {x, y + 1};
	if (x < mid)
		return {x + 1, y};
	else
		return {x - 1, y};
}

int findAss(int i)
{
	auto [x, y] = c[i];
	auto [nx, ny] = next(i);
	if (nx == mid && x != mid)
		return -1;
	return a[nx][ny];
}

bool move(int i)
{
	bool ok = false;
	auto [x, y] = c[i];
	auto [nx, ny] = next(i);
	if (a[nx][ny] != -1)
		return false;
	if (ny == r)
		ok = true;
	if (!ok)
		a[nx][ny] = i;
	a[x][y] = -1;
	c[i] = {nx, ny};
	int idx = p[i];
	if (nx == mid && x != mid)
	{
		p[i] = -1;
		if (idx != -1)
			add(idx, 1);
	}
	if (ok && idx != -1)
		add(idx, 1);
	while (idx != -1)
	{
		tie(nx, ny) = next(idx);
		assert(nx == x && ny == y);
		tie(x, y) = c[idx];
		assert(a[nx][ny] == -1);
		a[nx][ny] = idx;
		c[idx] = {nx, ny};
		a[x][y] = -1;
		idx = p[idx];
	}
	return ok;
}

int main()
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	
	
	FOR (i, 0, N) FOR (j, 0, N) a[i][j] = -1;
	fill(p, p + N * N, -1);
	
	int s;
	cin >> r >> s >> n;
		
	mid = s;
	FOR (i, 0, n)
	{
		int x, y;
		cin >> y >> x;
		y--;
		if (x <= mid)
			x--;
		c[i] = {x, y};
		a[x][y] = i;
		add(i, 0);
	}
	int ans = 0;
	int er = -1;
	while (true)
	{
		//if (ans > 7)
		//	break;
		//cerr << "Iter: " << ans << '\n';
		//FOR (i, 0, sz[0])
		//	cerr << heads[0][i] << ' ';
		//cerr << '\n';
		//FOR (i, 0, n)
		//{
		//	cerr << i << ' ' << c[i].F << ' ' << c[i].S << '\n';
		//}
		//cerr << "------------\n";
		FOR (i, 0, sz[0])
		{
			int h = heads[0][i];
			if (h == er)
			{
				erase(i, 0);
				i--;
				continue;
			}
			int x = findAss(h);
			if (x != -1)
			{
				assert(p[x] == -1);
				p[x] = h;
				erase(i, 0);
				i--;
			}
		}
		if (sz[0] == 0)
			break;
		er = -1;
		FOR (i, 0, sz[0])
		{
			int h = heads[0][i];
			auto [x, y] = c[h];
			if (x == mid)
			{
				if (move(h))
					er = h;
			}
		}
		FOR (i, 0, sz[0])
		{
			int h = heads[0][i];
			auto [x, y] = c[h];
			if (x != mid)
			{
				move(h);
			}
		}
		FOR (i, 0, sz[1])
			add(heads[1][i], 0);
		sz[1] = 0;
		ans++;
	}
	cout << ans << '\n';
	cerr << db(clock()) / CLOCKS_PER_SEC << '\n';
	return 0;
}