#include <bits/stdc++.h>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int n, k;
long long v[5000005];
int dq[5000005];
long long sum;
int main()
{
    fin >> n >> k;
    for(int i = 1; i <= n; i ++)
    {
        fin >> v[i];
    }
    int st = 0, dr = -1;
    for(int i = 1; i <= n; i ++)
    {
        if(dq[st] == i - k)
            st++;
        while(st <= dr && v[i] <= v[dq[dr]])
            dr--;
        dq[++dr] = i;
        if(i >= k)
            sum += v[dq[st]];
    }
    fout << sum << '\n';
}