#include <bits/stdc++.h>

using namespace std;

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

const int Nmax =  5e6 + 5;
int A[Nmax], D[Nmax];

int main()
{
    int N, K;
    in >> N >> K;
    for(int i = 1; i <= N; ++i)
        in >> A[i];
    int back = 1, front = 0; // heresy but it is what it is
    long long ans = 0;
    for(int i = 1; i <= N; ++i)
    {
        while(back <= front && A[i] <= A[D[front]])
            front--;
        front++;
        D[front] = i;
        if(i >= K)
        {
            ans += A[D[back]];
            if(D[back] == i - K + 1)
                back++;
        }
    }
    out << ans;
    return 0;
}