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

int main(){
    int n,m;
    cin >> n >> m;
    vector<int> nums(n);
    for(int i = 0;i<n;i++){
        nums[i] = i;
    }
    set<pair<int,int>> count;
    for(int i = 0;i<m;i++){
        int a;
        cin >> a;
        a--;
        int s = nums[a],t = nums[a+1];
        if(s>t) swap(s,t);
        count.insert({s,t});
        //cout << s << " " << t << endl;
        swap(nums[a],nums[a+1]);
    }
    cout << count.size() << endl;
}