/* -*- coding: utf-8 -*-
 *
 * 3091.cc:  No.3091 The Little Match Boy - yukicoder
 */

#include<cstdio>
#include<algorithm>
#include<utility>

using namespace std;

/* constant */

const int MAX_N = 100000;
const int MAX_M = 100000;

/* typedef */

using pii = pair<int,int>;

/* global variables */

int ss[MAX_M], ps[MAX_N];
pii es[MAX_M];

/* subroutines */

/* main */

int main() {
  int n, m;
  scanf("%d%d", &n, &m);
  for (int i = 0; i < n; i++) scanf("%d", ss + i), ss[i]--;

  for (int i = 0; i < n; i++) ps[i] = i;
  
  for (int i = 0; i < m; i++) {
    int u = ss[i], v = ss[i] + 1;
    int p0 = ps[u], p1 = ps[v];
    if (p0 > p1) swap(p0, p1);
    es[i] = {p0, p1};
    swap(ps[u], ps[v]);
  }
  
  sort(es, es + m);
  m = unique(es, es + m) - es;

  printf("%d\n", m);
  
  return 0;
}