package chelper;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import io.InputReader;
import io.OutputWriter;
import misc.GCJSolution;
import misc.SimpleSavingChelperSolution;


public class TaskB extends GCJSolution {

  public void solve(int testNumber, InputReader in, OutputWriter out) {
    wrapSolve(testNumber, in, out);
  }

  @Override
  public void solve(int testNumber) {
    int n = in.nextInt();
    int[] a = in.nextIntArray(n);

    List<Integer> even = new ArrayList<>();
    List<Integer> odd = new ArrayList<>();

    for (int i = 0; i < n; i++) {
      if (i % 2 == 0) {
        even.add(a[i]);
      } else {
        odd.add(a[i]);
      }
    }

    Collections.sort(even);
    Collections.sort(odd);

    for (int i = 0; i < n - 1; i++) {
      int x = i % 2 == 0 ? even.get(i / 2) : odd.get(i / 2);
      int y = (i + 1) % 2 == 0 ? even.get((i + 1) / 2) : odd.get((i + 1) / 2);

      if (x > y) {
        out.println(i);
        return;
      }
    }

    out.println("OK");
  }
}