#include <bits/stdc++.h>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
const int NMAX = 5e6 + 1;
int n, k, arr[NMAX];
long long sum = 0;
deque<int> dq;

int main()
{
    fin >> n >> k;
    for(int i = 1; i <= n; i++)
        fin >> arr[i];
    for(int i = 1; i <= k; i++)
    {
        while(!dq.empty() && arr[i] < dq.back())
            dq.pop_back();
        dq.push_back(arr[i]);
    }
    sum += dq.front();
    for(int i = 2; i + k - 1 <= n; i++)
    {
        while(!dq.empty() && arr[i + k - 1] < dq.back())
            dq.pop_back();
        dq.push_back(arr[i + k - 1]);
        if(arr[i - 1] == dq.front())
            dq.pop_front();
        sum += dq.front();
    }
    fout << sum;

    fin.close();
    fout.close();
    return 0;
}