#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;
typedef unsigned long long ull;
typedef long double ld;
int dx[8] = { 1, 0, -1, 0, 1, 1, -1, -1 }, dy[8] = { 0, 1, 0, -1, 1, -1, 1, -1 };
const long long mod = 998244353;
const ll inf = 1LL << 60;
const int INF = 5e8;

int main()
{
    ll n, m;
    cin >> n >> m;

    vector<ll> a(m);
    for (int i = 0; i < m; i++)
        cin >> a[i];

    ll ans = 0;

    map<ll, ll> mp;
    auto f = [&](auto self, ll x) {
        if (mp.count(x))
            return mp[x];
        if (x == 0)
            return 0LL;
        if (x == 1)
            return 1LL;
        ll ret = 0;
        if (x % 2 == 0) {
            ret = x;
        } else {
            ret = 2 * self(self, x / 2);
        }
        return mp[x] = ret;
    };

    for (int i = 0; i < m; i++) {
        ll x = a[i] - (i == 0 ? 0 : a[i - 1]) - 1;
        ans += f(f, x);
    }
    cout << ans << endl;
}