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

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

int n , k , i;
int a[5000001];
deque < int > dq;
long long sum;

int main()
{
    f >> n >> k;
    for ( i = 1; i <= n; i++ )
        f >> a[i];

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