#include <bits/stdc++.h>
#include <deque>

using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
const long long nmax=5000001;
int v[nmax];
int main()
{
    long long n,k,i,s=0;
    deque<long long> dq;
    fin >> n >> k;
    for(i=1;i<=n;i++)
        fin >> v[i];
    for(i=1;i<=n;i++)
    {
        while(!dq.empty() && dq.front() <= i - k)
            dq.pop_front();
        while(dq.size()>0 && v[i]<v[dq.back()])
            dq.pop_back();
        dq.push_back(i);
        if(i>=k)
            s+=v[dq.front()];
    }
    fout << s;
    return 0;
}