#include <bits/stdc++.h>

using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n,i,k,x;
deque<pair<int,int>> q;
int64_t sol;
int main()
{
    f>>n>>k;
    for(i=1;i<k;i++)
    {
        f>>x;
        while(q.size()&&x<=q.back().first)q.pop_back();
        q.push_back(make_pair(x,i));
    }
    for(;i<=n;i++)
    {
        f>>x;
        while(q.size()&&x<=q.back().first)q.pop_back();
        q.push_back(make_pair(x,i));
        if(q.front().second==i-k)
            q.pop_front();
        sol+=q.front().first;
    }
    g<<sol;
    return 0;
}