#include <stdio.h>
#include <atcoder/all>
#include <bits/stdc++.h>
using namespace std;
using namespace atcoder;
using mint = modint998244353;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf32 1000000001
#define Inf64 4000000000000000001LL

int main(){
	
	int n,m;
	cin>>n>>m;
	
	vector<int> p(n);
	rep(i,n)p[i] = i;
	vector<int> t(m);
	rep(i,m){
		cin>>t[i];
		t[i]--;
	}
	reverse(t.begin(),t.end());
	set<pair<int,int>> S;
	rep(i,m){
		int x = p[t[i]],y = p[t[i]+1];
		S.emplace(min(x,y),max(x,y));
		swap(p[t[i]],p[t[i]+1]);
	}
	cout<<S.size()<<endl;
	
	return 0;
}