#include <bits/stdc++.h>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int n, k;
int dq[5005005];
int v[5005005];
int main()
{
    fin >> n >> k;
    int st = 1, dr = 0;
    long long sum = 0;
    for(int i = 1; i <= n; i ++)
    {
        fin >> v[i];
        if(i - k == dq[st])
        {
            st ++;
        }
        while(st <= dr && v[i] <= v[dq[dr]])
            dr --;
        dq[++dr] = i;
        if(i >= k)
            sum += v[dq[st]];
    }
    fout << sum;
}