#include <fstream>

#define NMAX 5000005

using namespace std;

ifstream fin ("deque.in");
ofstream fout("deque.out");

int Deque[NMAX], st, dr, a[NMAX];

int main()
{
    int n, k;
    long long s = 0;
    fin >> n >> k;
    for(int i = 1; i <= n; ++i) fin >> a[i];

    st = dr = 1;
    Deque[1] = 1;
    for(int i = 2; i <= n; ++i)
    {
        while(st <= dr && a[i] <= a[Deque[dr]]) dr--;
        Deque[++dr] = i;

        if(i-Deque[st] >= k) st++;
        if(i >= k) s += a[Deque[st]];
    }
    fout << s;
    fin.close(); fout.close();
    return 0;
}


/*#include <fstream>
#include <deque>

using namespace std;

ifstream fin ("deque.in");
ofstream cout("deque.out");

deque<int> q;
int a[5000005];

int main()
{
    int n, k, x;
    long long s = 0;
    fin >> n >> k;
    for(int i = 1; i <= n; ++i) fin >> a[i];
    ///prelucrez primele k elemente
    for(int i = 1; i <= k; ++i)
    {
         x = a[i];
        /// scot din queue toate elem >= cu x;
        while(!q.empty() && x <= a[q.back()])
            q.pop_back();
        q.push_back(i);
    }
    s += a[q.front()];
    for(int i = k + 1; i <= n; ++i)
    {
        x = a[i];

        while(!q.empty() && x <= a[q.back()])
            q.pop_back();
        q.push_back(i);
        /// verific daca s-a invechit un elem
        if(i-q.front() >= k) q.pop_front();
        s += a[q.front()];
    }
    cout << s;
    return 0;
}*/