#include <fstream>
#include <iostream>
#include <deque>

using namespace std;

ifstream f ("deque.in");
ofstream g ("deque.out");


const int NMAX = 5e6;
int v[NMAX+1];

deque<int> dq;

int main()
{
    int n, k;
    f >> n >> k;
    long long sum = 0;
    for(int i=1; i<=n; i++){
        f >> v[i];
        if(!dq.empty() and i - k == dq.front())
            dq.pop_front();
        while(!dq.empty() and v[i] <= v[dq.back()])
            dq.pop_back();
        dq.push_back(i);
        if(!dq.empty() and i >= k)
            sum += v[dq.front()];
    }
    g << sum;
    return 0;
}