#include<bits/stdc++.h>
    #include <ext/pb_ds/tree_policy.hpp>
    #include <ext/pb_ds/assoc_container.hpp>
    using namespace std;
    using namespace __gnu_pbds;

    #define mod 1000000007


    /// Debugging shits start here... https://pastebin.com/K2DWYpnm

    void __print(int x) {cerr << x;}
    void __print(long x) {cerr << x;}
    void __print(long long x) {cerr << x;}
    void __print(unsigned x) {cerr << x;}
    void __print(unsigned long x) {cerr << x;}
    void __print(unsigned long long x) {cerr << x;}
    void __print(float x) {cerr << x;}
    void __print(double x) {cerr << x;}
    void __print(long double x) {cerr << x;}
    void __print(char x) {cerr << '\'' << x << '\'';}
    void __print(const char *x) {cerr << '\"' << x << '\"';}
    void __print(const string &x) {cerr << '\"' << x << '\"';}
    void __print(bool x) {cerr << (x ? "true" : "false");}

    template<typename T, typename V>
    void __print(const pair<T, V> &x) {cerr << '{'; __print(x.first); cerr << ','; __print(x.second); cerr << '}';}
    template<typename T>
    void __print(const T &x) {int f = 0; cerr << '{'; for (auto &i: x) cerr << (f++ ? "," : ""), __print(i); cerr << "}";}
    void _print() {cerr << "]\n";}
    template <typename T, typename... V>
    void _print(T t, V... v) {__print(t); if (sizeof...(v)) cerr << ", "; _print(v...);}
    #ifndef ONLINE_JUDGE
    #define debug(x...) cerr << "[" << #x << "] = ["; _print(x)
    #else
    #define debug(x...)
    #endif
    /// Debugging shits ends here...
    // templates
    /*#include<ext/pb_ds/assoc_container.hpp>
    #include<ext/pb_ds/tree_policy.hpp>
    using namespace __gnu_pbds;
    /*template <typename T>
    using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;*/

    /// Some frequent usable functions
    #define int                        long long
    void add(int &a,int b){a+=b;if(a>mod)a-=mod;}
    void sub(int &a,int b){a-=b;if(a<0)a+=mod;}
    void mul(int &a, int b) {a=1ll * a * b % mod;}
    template<typename T> T pow(T a,T b, long long m){T ans=1; while(b>0){ if(b%2==1) ans=(ans*a)%m; b/=2; a=(a*a)%m; } return ans%m; }
    int powmod(int a,int b)
    {int res = 1;while(b){if(b&1){res = (res * a)%mod;}b= b/2;a = (a*a)%mod;}return res;}

    int gcd(int a, int b, int &x, int &y) {if (a == 0) {x = 0; y = 1;return b;
    }int x1, y1;int d = gcd(b%a, a, x1, y1); x = y1 - (b / a) * x1;y = x1;return d;}
    //int find(int v){return v==parent[v]?v:parent[v] = find(parent[v]);}
    // void merge(int i,int j)
    // {i = find(i);j = find(j);if(i == j)return;parent[parent[i]] = parent[j];cmp--;}

    // Directions.......
    /* int dx[] = {1,-1,0,0} , dy[] = {0,0,1,-1}; */ // 4 Direction
    /* int dx[] = {1,-1,0,0,1,1,-1,-1} , dy[] = {0,0,1,-1,1,-1,1,-1}; */ // 8 Direction
    /* int dx[] = {1,-1,1,-1,2,2,-2,-2} , dy[] = {2,2,-2,-2,1,-1,1,-1}; */ // Knight moves
    /* int dx[] = {2,-2,1,1,-1,-1} , dy[] = {0,0,1,-1,1,-1}; */ // Hexagonal Direction
    #define fast ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL)
    #define sp(a , x) cout << fixed << setprecision(a) << x << endl;
    #define endl "\n"
    #define pb push_back
    #define pf push_front
    #define ub upper_bound
    #define lb lower_bound
    #define F first
    #define S second
    #define mset(a, b) memset(a, b, sizeof a)
    #define sz(x) ((ll)(x.size()))
    #define sqr(x) ((x) * (x))
    #define graph vector<int>
    #define vi vector<int>
    #define vvi vector<vector<int>>
    #define pi pair<int,int>
    #define all(c)                      c.begin() , c.end()
    #define rep(i,a,b) for(int i=a;i<=b;i++)
    #define rrep(i,a,b) for(int i=a;i>=b;i--)
    #define iter(it,a) for(auto it=a.begin();it!=a.end();it++)
    #define PQP priority_queue<pi, vector<pi>, greater<pi>>
    #define PQI priority_queue<int, vector<int>, greater<int>>
    #define dbg debug
    #define inf (int)1e16
    const long double EPS = 0.0000000001;
    const long double PI = (acos(-1));


    /// define some data.......

  const int N = (int)2e6+5;
  int n,k;
  int a[N];
  int dp[N];
   void solve()
 {
   cin >> n >> k;

   rep(i,1,n)
   {
     cin >> a[i];
     dp[i] = a[i];
   }

   int no_of_blocks = (n + k -1)/k;

   for(int i=2;i<=no_of_blocks;i++)
   {
     int l = max(1ll , ((i-2)*k) + 1);
     int r = min(n , (i-1)*k);
     int mx_1 , mx_2;
     mx_1 = mx_2 = -inf;
     int id1 , id2 = 0;
     for(int j=l;j<=r;j++)
     {
       if(dp[j] >= mx_1)
       {
         mx_2 = mx_1;
         id2 = id1;
         mx_1 = dp[j];
         id1 = j;
       }
       else if(dp[j] > mx_2)
       {
         mx_2 = dp[j];
         id2 = j;
       }
     }

     l = ((i-1)*k)+1 , r = min(i*k,n);

     for(int j = l;j<=r;j++ )
     {
       dp[j] = max(dp[j] , dp[max(0ll , j - 2*k)]+a[j]);

       if((j-id1) != k)
       {
         dp[j] = max(dp[j] , mx_1 + a[j]);
       }

       if((j - id2) != k)
       {
         dp[j] = max(dp[j] , mx_2 + a[j]);
       }
     }
   }

     int ans = 0;
     rep(i,1,n)
     {
       ans = max(ans , dp[i]);
     }

     cout<<ans<<"\n";
 }

    int32_t main(){
         fast;
      int test=1;
      //cin >> test;
       int t=1;
       while(test--)
       {
         solve();
         mset(a,0);
         mset(dp,0);
       }

    }