#include <bits/stdc++.h>
#define NMAX 5000005

using namespace std;

int v[5000007];
deque<int>dq;

int main()
{
    ifstream fin("deque.in");
    ofstream fout("deque.out");
    int n,k;
    long long s = 0;
    fin >> n >> k;
    for(int i = 1;i <= n;i++)
    {
        fin >> v[i];
        while(!dq.empty() && v[i] <= v[dq.back()])
            dq.pop_back();
        dq.push_back(i);
        if(dq.front() == i - k)
            dq.pop_front();
        if(i >= k)
            s += v[dq.front()];
    }
    fout << s;
    return 0;
}