// Skyqwq
#include <bits/stdc++.h>

#define pb push_back
#define fi first
#define se second
#define mp make_pair

using namespace std;

typedef long long LL;
typedef pair<int, int> PII;

template <typename T> bool chkMax(T &x, T y) { return (y > x) ? x = y, 1 : 0; }
template <typename T> bool chkMin(T &x, T y) { return (y < x) ? x = y, 1 : 0; }

template <typename T> void inline read(T &x) {
    int f = 1; x = 0; char s = getchar();
    while (s < '0' || s > '9') { if (s == '-') f = -1; s = getchar(); }
    while (s <= '9' && s >= '0') x = x * 10 + (s ^ 48), s = getchar();
    x *= f;
}

const int N = 2005, S = 17;

int n, k, m, f[S][N];

PII e[N * N];

int g[N][N];

void inline add(int i, int j) {
	if (i + 1 >= j || g[i][j] || i < 0 || j >= n) return;
	g[i][j] = 1;
	e[++m] = mp(i, j);
}

struct W{
	int m, u, v, P, Q, Z;
} G[S][N];

void inline work() {
	memset(f, 0x3f, sizeof f);
	for (int i = 0; i <= k; i++) f[i][0] = f[i][1] = 0;
	for (int i = 1; i <= n; i++)
		f[1][i] = 1ll * (i - 1) * (i - 2) / 2;
	for (int i = 2; i <= n; i++) {
		if (i <= 3) {
			f[2][i] = 0;
			continue;
		}
		int A = (i - 1) / 2;
		f[2][i] = f[2][A] + f[2][i - A - 1] + i - 3;
	}
	for (int j = 3; j <= k; j++) {
		for (int i = 1; i <= n; i++) {
			if (i <= j + 1) {
				f[j][i] = 0;
				continue;
			}
			f[j][i] = f[j - 1][i];
			int le = 3, re = i;
			if (i >= 100) {
				int ot = 50;
				if (j >= 10) ot = 200;
				if (j == 14) ot = 400;
				if (j == 15) ot = 500;
				chkMin(re, G[j][i - 1].m + ot);
				chkMax(le, G[j][i - 1].m - ot);
			}
			for (int m = le; m <= re; m++) {
				int L = max((i - (m - 1)) / m, 0), R = min((i - (m - 1)) / 2, n);
				int lim = j <= 5 ? 5 : 1;
				chkMax(L, G[j][i - 1].u - lim);
				chkMin(R, G[j][i - 1].u + lim);
				
				for (int u = L; u <= R; u++) {
					for (int v = u; v <= u + 1; v++) {
						int le = (i - (m - 1) - u - v);
						if (le < 0) continue;
						int c = f[j][u] + f[j][v] + max(u - 1, 0) + max(v - 1, 0);
						c += f[j - 2][m - 1] + m - 2;
						
						int P = le / (m - 2), Q = le % (m - 2);
						int Z = m - 2 - Q;
						c += f[j][P] * Z + Z * (max(2 * P - 2, 0));
						c += f[j][P + 1] * Q + Q * (2 * P);
						if (chkMin(f[j][i], c))
						 	G[j][i] = (W) { m, u, v, P, Q, Z };	
					}
					
				}
			}
		}
	}
}

vector<int> ed[N];

int F[N];

void inline chk() {
	for (int i = 1; i <= m; i++)
		ed[e[i].fi].pb(e[i].se);
	for (int i = 0; i + 1 < n; i++) ed[i].pb(i + 1);
	for (int i = 0; i < n; i++) {
		memset(F, 0x3f, sizeof F);
		F[i] = 0;
		for (int u = i; u < n; u++) {
			if (F[u] > k) cout << i << " " << u << "???" << F[u] << endl;
			assert(F[u] <= k);
			for (int v: ed[u]) chkMin(F[v], F[u] + 1);
		}
	}
}

void inline link(int k, vector<int> a) {
	int n = a.size();
	if (n <= k + 1) return;
	
	if (k == 1) {
		for (int i = 0; i < n; i++)
			for (int j = i + 2; j < n; j++)
				add(a[i], a[j]);
		return;
	}
	if (k == 2) {
		int mid = n >> 1;
		vector<int> A, B;
		for (int i = 0; i < mid; i++) {
			add(a[i], a[mid]);
			A.pb(a[i]);
		}
		for (int i = mid + 1; i < n; i++)
			add(a[mid], a[i]), B.pb(a[i]);
		link(k, A), link(k, B);
		return;
	}
	if (k > 1 && f[k][n] == f[k - 1][n]) {
		link(k - 1, a);
		return;
	}
	W o = G[k][n];
	int m = o.m, u = o.u, v = o.v, P = o.P, Q = o.Q, Z = o.Z;
	vector<int> key, le, re;
	for (int i = 0; i < u; i++)
		add(a[i], a[u]), le.pb(a[i]);
	link(k, le);
	for (int i = n - v; i < n; i++)
		add(a[n - v - 1], a[i]), re.pb(a[i]);
	link(k, re);
	key.pb(a[u]);
	int num = u;
	for (int i = 1; i <= m - 2; i++) {
		int la = num;
		num += P + 1;
		if (i <= Q) num++;
		vector<int> now;
		int X = la, Y = num;
		for (int j = X + 1; j < Y; j++) now.pb(a[j]), add(a[X], a[j]), add(a[j], a[Y]);
		link(k, now);
		key.pb(a[num]);
	}
	for (int i = 0; i + 1 < key.size(); i++) add(key[i], key[i + 1]);
	link(k - 2, key);
}

int main() {
	read(n), read(k); ++n;	
	work();
	vector<int> t;
	for (int i = 0; i < n; i++) t.pb(i);
	link(k, t);
	printf("%d\n", m); //chk(); return 0;
	for (int i = 1; i <= m; i++) printf("%d %d\n", e[i].fi, e[i].se);
    return 0;
}