#include <bits/stdc++.h>

using namespace std;

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

int main()
{
    deque<int> D;
    int N, K;
    in >> N >> K;
    vector<int> A(N + 1);
    for(int i = 1; i <= N; ++i)
    {
        in >> A[i];
    }
    long long ans = 0;
    for(int i = 1; i <= N; ++i)
    {
        while(!D.empty() && A[i] <= A[D.back()])
        {
            D.pop_back();
        }
        D.push_back(i);
        if(i >= K)
        {
            ans += A[D.front()];
            /*for(auto i : D)
            {
                out << A[i] << " ";
            }
            out << " " <<  A[D.front()] << '\n';*/
            if(D.front() == i - K + 1)
            {
                D.pop_front();
            }
        }
    }
    out << ans;
    return 0;
}