#include <iostream>
#include <cstdio>
#include <iostream>
#include <deque>
#define MAX 5000000

using namespace std;
int n, k;
int vec[MAX];
deque<int> dq;
long long suma;
int f=1, b;

void read()
{
    scanf("%d %d\n", &n, &k);
    for (int i=0; i<n; i++)
        scanf("%d\n", &vec[i]);
    for (int i=0; i<k-1; i++)
    {
        while(!dq.empty() && vec[dq.back()] > vec[i])
            dq.pop_back();
        dq.push_back(i);
    }

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

int main()
{
    freopen("deque.in", "r", stdin);
    freopen("deque.out", "w", stdout);
    read();
    cout<<suma;
    return 0;
}