#include <bits/stdc++.h>

using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
deque<pair<long long,int>> q;
long long n,k,x,y,s;
int main()
{
    in>>n>>k;
    for(int i=1;i<=n;i++)
    {
        in>>x;
        while(!q.empty()&&q.front().second<i-k+1) q.pop_front();
        if(x<q.front().first) q.push_front({x,i});
        else
        {
            while(x<=q.back().first&&!q.empty())
            {
                y=q.back().first;
                q.pop_back();
            }
            q.push_back({x,i});
        }
        if(i>=k) s+=q.front().first;
    }
    out<<s;
    return 0;
}