#include <bits/stdc++.h>
using namespace std;

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

/**
*/
deque<int> q;
int n , a[5000005] , k;

int main()
{
    int i , x;
    long long suma;
    fin >> n >> k;
    for(i = 1;i <= n;i++)
        fin >> a[i];
    for(i = 1;i <= k;i++)
    {
        x = a[i];
        while(!q.empty() and x <= a[q.back()])
            q.pop_back();
        q.push_back(i);
    }
    suma = a[q.front()];
    for(i = k + 1;i <= n;i++)
    {
        x = a[i];
        while(!q.empty() and x <= a[q.back()])
            q.pop_back();
        q.push_back(i);
        if(q.front() == i - k) q.pop_front();
        suma += a[q.front()];
    }
    fout << suma;
    return 0;
}