#include <bits/stdc++.h>
using namespace std;

const int MXN = 50005;
int N, M, perm[MXN], ans, rev[MXN];
bitset<MXN> bs[MXN], cur;

int main() {
  cin >> N >> M;
  for (int i(0); i != N; ++i) cin >> perm[i], --perm[i], rev[perm[i]] = i;
  for (int i(N - 2); ~i; --i) {
    bs[rev[i]] = bs[rev[i + 1]];
    bs[rev[i]].set(rev[i + 1]);
  }
  for (int i(0); i != N; ++i) bs[i] >>= i;
  for (int i(0); i * M < N; ++i) {
    for (int j(i * M + M - 2); j >= i * M; --j) bs[j] &= bs[j + 1];
    cur.set();
    for (int j(i * M); j != i * M + M; ++j) {
      ans += (bs[j] & cur).count();
      if (j + M == N) break;
      cur &= bs[j + M];
    }
  }
  cout << ans << endl;
  return 0;
}