#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return true; } return false; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return true; } return false; }
#define all(x) (x).begin(),(x).end()
#define fi first
#define se second
#define mp make_pair
#define si(x) int(x.size())
const int mod=998244353,MAX=300005,INF=1<<30;

int main(){
    
    std::ifstream in("text.txt");
    std::cin.rdbuf(in.rdbuf());
    cin.tie(0);
    ios::sync_with_stdio(false);
    
    ll N,M;cin>>N>>M;
    vector<ll> A(M);
    for(int i=0;i<M;i++) cin>>A[i];
    ll ans=N-M;
    
    for(int i=0;i+1<M;i++){
        ll diff=A[i+1]-A[i];
        ll can=1;
        while(diff>2&&diff%2==0){
            can*=2;
            diff/=2;
        }
        ans-=can-1;
    }
    
    cout<<ans<<endl;
}