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

deque <int> a;
int i, k, ok, n, t, minn, j, v[5000002];
long long sum;

int main()
{
    ifstream fin("deque.in");
    ofstream fout("deque.out");
    fin>>n>>k;
    for(i=1; i<=n; i++)
    {
        fin>>v[i];
    }

    for(i=1; i<=n; i++)
    {

        while(a.empty()==false && v[a.back()]>=v[i]) a.pop_back();
        a.push_back(i);
        if(a.front()==i-k) a.pop_front();

        if(i>=k) sum+=v[a.front()];
    }

    fout<<sum;

    return 0;
}