#include<bits/stdc++.h>
using namespace std;
///------------------------------
ifstream in("deque.in");
ofstream out("deque.out");
///------------------------------
deque<pair<int,int> >dq;
int v[5000005];


int main()
{
    int n,k,l;
    in>>n>>k;
    for(int i=1; i<=n; i++)
        in>>v[i];
    for(int i = 1; i <= k; ++i)
    {
        while(!dq.empty() && v[i] <= dq.back().first)
            dq.pop_back();
        dq.push_back({v[i],i});
    }
    long long r = dq.front().first;
    for(int i = k+1; i <= n; ++i)
    {
        while(!dq.empty() && v[i] <= dq.back().first)
            dq.pop_back();
        dq.push_back({v[i],i});
        if(dq.front().second<i - k + 1)
            dq.pop_front();
        r += dq.front().first;
    }
    out<<r;
    return 0;
}