#include <bits/stdc++.h>

using namespace std;

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

int n, k;
long long v[500500];
int dq[500500];
int st = 0, dr = -1;

int main()
{
    fin >> n >> k;
    for(int i = 1; i <= n; i ++)
    {
        fin >> v[i];
    }
    long long sum = 0;
    for(int i = 1; i <= n; i ++)
    {
        if(dq[st] == i - k)
            st++;
        while(st <= dr && v[dq[dr]] >= v[i])
        {
            dr--;
        }
        dq[++dr] = i;
        if(i >= k)
            sum = sum + v[dq[st]];
    }
    sum = sum + v[dq[st]];
    fout << sum << '\n';
    return 0;
}