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

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


int back = 0, front = 1;
int deque[5000010];
int v[5000010];

void push_back(int x)
{
    ++back;
    deque[back] = x;
}

void pop_front()
{
    ++front;
}

void pop_back()
{
    --back;
}

int get_front()
{
    return deque[front];
}

int get_back()
{
    return deque[back];
}

bool is_Empty()
{
    return (front > back);
}

int main()
{
    int N, K;
    long long sum = 0;
    fin >> N >> K;
    for(int i=0; i<N; ++i)
        fin >> v[i];
    for(int i=0; i<N; ++i)
    {
        while(!is_Empty() && v[i] <= v[get_back()])
        {
            pop_back();
        }
        push_back(i);

        if(i-K == get_front())
            pop_front();
        if(i>=K-1)
            sum += v[get_front()];
    }

    fout << sum;
    return 0;
}