#include <iostream>
#include <fstream>
#include <deque>
using namespace std;

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

const int nmax = 5e6+5;
deque <int> d;
int v[nmax], n, k;
long long sol;

int main() {
    ios_base::sync_with_stdio(false);
    int i;
    fin >> n >> k;
    for(i=1; i<=n; i++)
        fin >> v[i];
    for(i=1; i<=n; i++) {
        while(!d.empty() && v[i]<=v[d.back()]) {
            d.pop_back();
        }
        d.push_back(i);
        if(d.front()==i-k) d.pop_front();
        if(i>=k) sol+=v[d.front()];
    }
    fout << sol;
    fin.close();
    fout.close();
    return 0;
}