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

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

long long s, a[5000001];
int n, k;
deque <int> T;

int main()
{
    f>>n>>k;
    for(int i=0; i<n; i++)
    {
        f>>a[i];
        while(!T.empty() && a[i]<=a[T.back()])
            T.pop_back();
        T.push_back(i);
        if(T.front()==i-k)
        {
            T.pop_front();
        }
        if(i>=k-1)
        {
            s+=a[T.front()];
        }
    }
    g<<s;
    return 0;
}