#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
template <class T>
using vc = vector<T>;
template <class T>
using vvc = vc<vc<T>>;
#define overload4(a, b, c, d, name, ...) name
#define rep1(n) for (ll i = 0; i < n; ++i)
#define rep2(i, n) for (ll i = 0; i < n; ++i)
#define rep3(i, a, b) for (ll i = a; i < b; ++i)
#define rep4(i, a, b, c) for (ll i = a; i < b; i += c)
#define rep(...) overload4(__VA_ARGS__, rep4, rep3, rep2, rep1)(__VA_ARGS__)
#define all(i) begin(i), end(i)
bool chmin(auto &a, const auto &b) {
    if (a <= b) return 0;
    a = b;
    return 1;
}
bool chmax(auto &a, const auto &b) {
    if (a >= b) return 0;
    a = b;
    return 1;
}
void solve();
int main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(20);
    ll t = 1;
    // cin >> t;
    for (int i = 1; i <= t; i++) solve();
    return 0;
}
ll dy[] = {0, 1, 0, -1}, dx[] = {1, 0, -1, 0};
void solve() {
    ll n, m;
    cin >> n >> m;
    vector<ll> a(m);
    rep(i, n) cin >> a[i], a[i]--;
    vector<ll> cur(n);
    iota(all(cur), 0);
    set<pair<ll, ll>> st;
    for (auto x : a) {
        swap(cur[x], cur[x + 1]);
        st.insert({min(cur[x], cur[x + 1]), max(cur[x], cur[x + 1])});
    }
    cout << st.size() << endl;
}