#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for(int i = 0; i < n; i++)
#define rep2(i, x, n) for(int i = x; i <= n; i++)
#define rep3(i, x, n) for(int i = x; i >= n; i--)
#define each(e, v) for(auto &e: v)
#define pb push_back
#define eb emplace_back
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define sz(x) (int)x.size()
using ll = long long;
using pii = pair<int, int>;
using pil = pair<int, ll>;
using pli = pair<ll, int>;
using pll = pair<ll, ll>;
const int MOD = 1000000007;
//const int MOD = 998244353;
const int inf = (1<<30)-1;
const ll INF = (1LL<<60)-1;
template<typename T> bool chmax(T &x, const T &y) {return (x < y)? (x = y, true) : false;};
template<typename T> bool chmin(T &x, const T &y) {return (x > y)? (x = y, true) : false;};

struct io_setup{
    io_setup(){
        ios_base::sync_with_stdio(false);
        cin.tie(NULL);
        cout << fixed << setprecision(15);
    }
} io_setup;

int main(){
    int N, M; cin >> N >> M;

    vector<int> A(N);
    rep(i, N) cin >> A[i];
    vector<int> v(N+1, 0);

    rep(i, M) v[A[i]]++;

    vector<bool> ok(N+1, false);
    rep(i, N+1){
        if(v[i] == 0) ok[i] = true;
    }

    rep(i, N-M){
        int l = A[i], r = A[M+i];

        v[r]++, v[l]--;
        if(v[l] == 0) ok[l] = true;
    }

    rep(i, N+1){
        if(ok[i]) {cout << i << '\n'; return 0;}
    }
}
#include<bits/stdc++.h>
using namespace std;
// #include <ext/pb_ds/assoc_container.hpp> 
// #include <ext/pb_ds/detail/standard_policies.hpp>
// using namespace __gnu_pbds;

#pragma GCC optimize("O3")
#ifdef LOCAL
#include "/Users/lbjlc/Desktop/coding/debug_utils.h"
#else
#define print(...) ;
#define printn(...) ;
#define printg(...) ;
#define fprint(...) ;
#define fprintn(...) ;
#endif

#define rep(i, a, b) for(auto i = (a); i < (b); i++)
#define rrep(i, a, b) for(auto i = (a); i > (b); i--)
#define all(v) (v).begin(), (v).end()
#define pb push_back
// #define mp make_pair
#define fi first
#define se second
#define maxi(x, y) x = max(x, y)
#define mini(x, y) x = min(x, y)
// long long fact(long long n) { if(!n) return 1; return n*fact(n-1); }
// #define endl '\n'
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
int get_random() {
    static uniform_int_distribution<int> dist(0, 1e9 + 6);
    return dist(rng);
}
#define solve_testcase int T;cin>>T;for(int t=1;t<=T;t++){solve(t);}


typedef unsigned long long ull;
typedef long long ll;
 
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<double, double> pdd;
 
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<vvi> vvvi;
typedef vector<pii> vpii;
typedef vector<pll> vpll;
typedef vector<pdd> vpdd;
typedef vector<long long> vll;
#define bd(type,op,val) bind(op<type>(), std::placeholders::_1, val)

template<class T>
void make_unique(T & v) {
    sort(v.begin(), v.end()); v.erase(unique(v.begin(), v.end()), v.end());
}
int geti() { int x; cin >> x; return x; }
long long getll() { long long x; cin >> x; return x; }
double getd() { double x; cin >> x; return x; }
// pair<int, int> a(geti(), geti()) does not work
// pair<int, int> a({geti(), geti()}) works, since it uses initializer.

const int MAXN = 3e5 + 100;

void solve(int tt) {
    // cout<<"Case #"<<tt<<": ";
}

ll cal(int n, int tot) {
	if(n+n<tot) return 0;
	if(n<tot) return n-(tot-n)+1;
	return tot-1;
}

int main(int argc, char * argv[]) {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
    // solve_testcase;

    int n,k;
    cin>>n>>k;
    k=abs(k);

    long long res=0;
    rep(i,2,2*n+1) {
    	res+=cal(n,i)*cal(n,i+k);
    }
    cout<<res<<endl;



    return 0;
}











