#define __USE_MINGW_ANSI_STDIO 0
#include<stdio.h>
int u[100005], v[100005];
int h[100005], l;
int comp_h(int a, int b)
{
	if (u[h[a]] > u[h[b]])
		return 1;
	else if (u[h[a]] < u[h[b]])
		return -1;
	else if (v[h[a]] > v[h[b]])
		return 1;
	else
		return -1;
}
void swap_h(int a, int b)
{
	int f = h[a];
	h[a] = h[b];
	h[b] = f;
	return;
}
void push(int ne)
{
	h[l] = ne;
	int p = l++;
	for (; p > 0; p = (p - 1) / 2)
		if (comp_h((p - 1) / 2, p) > 0)
			swap_h((p - 1) / 2, p);
	return;
}
int pop()
{
	swap_h(0, --l);
	int p = 0;
	for (;;)
	{
		if (2 * p + 2 < l)
		{
			if (comp_h(2 * p + 1, 2 * p + 2) > 0)
			{
				if (comp_h(p, 2 * p + 2) > 0)
					swap_h(p, 2 * p + 2);
				p = 2 * p + 2;
			}
			else
			{
				if (comp_h(p, 2 * p + 1) > 0)
					swap_h(p, 2 * p + 1);
				p = 2 * p + 1;
			}
		}
		else if (2 * p + 1 < l)
		{
			if (comp_h(p, 2 * p + 1) > 0)
				swap_h(p, 2 * p + 1);
			p = 2 * p + 1;
		}
		else
			break;
	}
	return h[l];
}
int s[100005];
int p[100005];
int main()
{
	int n, m;
	scanf("%d %d", &n, &m);
	int i;
	for (i = 0; i < m; i++)
		scanf("%d", &s[i]);
	for (i = 0; i < n; i++)
		p[i] = i;
	for (i = 0; i < m; i++)
	{
		s[i]--;
		u[i] = p[s[i]];
		v[i] = p[s[i] + 1];
		if (u[i] > v[i])
		{
			u[i] ^= v[i];
			v[i] ^= u[i];
			u[i] ^= v[i];
		}
		p[s[i]] ^= p[s[i] + 1];
		p[s[i] + 1] ^= p[s[i]];
		p[s[i]] ^= p[s[i] + 1];
	}
	l = 0;
	for (i = 0; i < m; i++)
		push(i);
	for (i = 0; i < m; i++)
		p[i] = pop();
	int ans = 1;
	for (i = 1; i < m; i++)
		if (u[p[i]] != u[p[i - 1]] || v[p[i]] != v[p[i - 1]])
			ans++;
	printf("%d\n", ans);
	return 0;
}