#include <iostream>
#include <fstream>
#include <vector>
#include <stack>
#include <unordered_map>
#include <algorithm>
#define inf 99999999999

using namespace std;

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

const int N = 5e6+1;

deque <long long int > stiva;

int n, k , v[N];

void solve() 
{
    in >> n >> k;
    long long int s = 0;
    for (int i = 1; i <= k; i++)
    {
        in >> v[i];
        while (!stiva.empty() && stiva.back() < i - k + 1)
            stiva.pop_back();
        while (!stiva.empty() && v[i] <= v[stiva.front()])
            stiva.pop_front();
        stiva.push_front(i);
    }
    s += v[stiva.back()];
    for (int i = k+1; i <= n; i++)
    {
        in >> v[i];
        while (!stiva.empty() && stiva.back() < i - k + 1)
            stiva.pop_back();
        while ( !stiva.empty() && v[i] <= v[stiva.front()])
            stiva.pop_front();
        stiva.push_front(i);
        s += v[stiva.back()];
    }
    out << s;
}

int main()
{
    int task = 1;
    while (task--)
        solve();
}