#ifndef LOCAL
    #pragma GCC optimize("Ofast")
#endif

#ifdef LOCAL
    #define _GLIBCXX_DEBUG
#endif

#include <bits/stdc++.h>
#define pb push_back
#define pii pair<int, int>
using ll = long long;
using ci = const int;
using cll = const long long;

using namespace std;

/*******************************/
// INPUT / OUTPUT

#ifndef LOCAL
    ifstream in("deque.in");
    ofstream out("deque.out");
    #define cin in
    #define cout out
#endif
/*******************************/
/// GLOBAL DECLARATIONS

int N, K;
ll rasp;

struct TwoStacks
{
    stack <pii> st, dr;

    inline void push_back(int x)
    {
        if (st.empty())
            st.push({x, x});
        else
            st.push({x, min(st.top().second, x)});
    }

    inline void pop_front()
    {
        if (dr.empty())
        {
            while (!st.empty())
            {
                pii top = st.top();
                st.pop();

                if (dr.empty())
                    dr.push({top.first, top.first});
                else
                    dr.push({top.first, min(top.first, dr.top().second)});
            }
        }

        dr.pop();
    }

    inline int get_min()
    {
        if (st.empty() && dr.empty()) return -1;
        if (st.empty()) return dr.top().second;
        if (dr.empty()) return st.top().second;
        return min(st.top().second, dr.top().second);
    }
};
/*******************************/
/// FUNCTIONS

void ReadInput();
void Solution();
void Output();
/*******************************/
///-------------------------------------
inline void ReadInput()
{
    cin >> N >> K;
}
///-------------------------------------
inline void Solution()
{
    int x;
    TwoStacks ts;
    for (int i = 1 ; i <= K ; ++ i)
    {
        cin >> x;

        ts.push_back(x);
    }
    
    rasp += 1LL * ts.get_min();

    for (int i = K + 1 ; i <= N ; ++ i)
    {
        cin >> x;

        ts.push_back(x);
        ts.pop_front();

        rasp += 1LL * ts.get_min();
    }
}
///-------------------------------------
inline void Output()
{
    cout << rasp;
}
///-------------------------------------
int main()
{
    #ifndef LOCAL
        ios::sync_with_stdio(false);
        cin.tie(NULL);
        cout.tie(NULL);
    #endif
    ReadInput();
    Solution();
    Output();
    return 0;
}