#include <bits/stdc++.h>
using namespace std;
template <class T>
bool umin(T &a, T b) {
  return a > b ? (a = b, true) : false;
}
template <class T>
bool umax(T &a, T b) {
  return a < b ? (a = b, true) : false;
}
long long POW(long long a, long long p, long long M) {
  if (!p) return 1LL;
  long long T = POW(a, p / 2, M);
  T = T * T % M;
  if (p & 1) T = T * (a % M) % M;
  return T;
}
long long SQRT(long long a) {
  long long b = (long long)sqrtl(((double)a) + 0.5);
  while (b * b < a) ++b;
  while (b * b > a) --b;
  return (b * b == a) ? b : -1;
}
const long long MOD = 1e9 + 7;
signed main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  cout.precision(10);
  cout << fixed;
  long long n, m;
  cin >> n >> m;
  if (n == 1) {
    cout << 0 << endl;
    return 0;
  }
  vector<vector<long long>> guess(n + 1);
  long long f = 0;
  long long N = 2e5;
  long long fq[4 * N];
  memset(fq, 0, sizeof(fq));
  for (long long i = 1; i <= n; i++) fq[N + i] = 1;
  for (long long i = 1; i <= n; i++) {
    long long mx = min(n, i + m + 1);
    f += 2 * (mx - i + 1) - 1;
  }
  long long st;
  for (long long i = 1; i <= m; i++) {
    long long a;
    cin >> a;
    guess[a].push_back(i);
  }
  for (long long i = 1; i <= n; i++) {
    if (guess[i].empty()) continue;
    long long ss = guess[i][0];
    for (long long j = 1; j <= guess[i].size(); ++j) {
      if (j < guess[i].size() && guess[i][j] == guess[i][j - 1] + 1)
        continue;
      else {
        long long ct = 0;
        for (long long k = i - ss; k >= i - guess[i][j - 1]; --k) {
          long long org = min(n, k + m + 1);
          long long wt = min(n, k + m - (guess[i][j - 1] + (k - i) + 1) + 1);
          f -= fq[N + k] * (org - wt);
          ct += fq[N + k];
          fq[N + k] = 0;
        }
        fq[N + i - guess[i][j - 1] - 1] += ct;
        if (j < guess[i].size()) ss = guess[i][j];
      }
    }
  }
  memset(fq, 0, sizeof(fq));
  for (long long i = 1; i <= n; i++) fq[i] = 1;
  for (long long i = n; i >= 1; i--) {
    if (guess[i].empty()) continue;
    long long ss = guess[i][0];
    for (long long j = 1; j <= guess[i].size(); ++j) {
      if (j < guess[i].size() && guess[i][j] == guess[i][j - 1] + 1)
        continue;
      else {
        long long ct = 0;
        for (long long k = i + ss; k <= i + guess[i][j - 1]; ++k) {
          long long org = max(1LL, k - m - 1);
          long long wt = max(1LL, k - m + (guess[i][j - 1] - (k - i) + 1) - 1);
          f -= fq[k] * (wt - org);
          ct += fq[k];
          fq[k] = 0;
        }
        fq[i + guess[i][j - 1] + 1] += ct;
        if (j < guess[i].size()) ss = guess[i][j];
      }
    }
  }
  cout << f << endl;
  cerr << "Time elapsed: " << 1.0 * clock() / CLOCKS_PER_SEC << " s\n";
  return 0;
}
