#include <bits/stdc++.h>
//#include <atcoder/all>
using namespace std;
// using namespace atcoder;
// using mint = modint1000000007;
// const int mod = 1000000007;
// using mint = modint998244353;
// const int mod = 998244353;
// const int INF = 1e9;
// const long long LINF = 1e18;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep2(i, l, r) for (int i = (l); i < (r); ++i)
#define rrep(i, n) for (int i = (n)-1; i >= 0; --i)
#define rrep2(i, l, r) for (int i = (r)-1; i >= (l); --i)
#define all(x) (x).begin(), (x).end()
#define allR(x) (x).rbegin(), (x).rend()
#define P pair<int, int>
template<typename A, typename B> inline bool chmax(A& a, const B& b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A& a, const B& b) { if (a > b) { a = b; return true; } return false; }

int main() {
	std::ios::sync_with_stdio(false);
	std::cin.tie(nullptr);
	int n, k; cin >> n >> k;
	vector<int>p(n);
	rep(i, n)cin >> p[i], p[i]--;
	vector<P>ans;
	rep(m, k) {
		int idx = m;
		while (idx < n) {
			int mn = idx;
			for (int i = idx; i < n; i += k) {
				if (p[i] < p[mn])mn = i;
			}
			while (mn != idx) {
				swap(p[mn], p[mn - k]);
				ans.emplace_back(mn - k, mn);
				mn -= k;
			}
			idx += k;
		}
	}
	rep(i, n)if (p[i] != i) {
		cout << -1 << endl;
		return 0;
	}
	cout << ans.size() << endl;
	for (auto [f, s] : ans)cout << f + 1 << " " << s + 1 << endl;
	return 0;
}