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

using namespace std;

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

deque <int> Q;
int n, k;
long long s;
int V[5000005];

void citire()
{
    f>>n>>k;
    for(int i=1; i<=n; i++){
        f>>V[i];
    }
}

void rez()
{
    int i;

    Q.push_back(1);
    for(i=2; i<=n; i++){
        if(Q.front() == i - k)
            Q.pop_front();
        while( !Q.empty() && (V[Q.back()] > V[i])){
            Q.pop_back();
        }

        Q.push_back(i);

        if(i >= k)
            s += V[Q.front()];
    }

    g<<s<<"\n";
}

int main()
{
    citire();
    rez();
    return 0;
}