///Buzatu Giulian
#include <bits/stdc++.h>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
const int NMAX=5000005;
int n,k,v[NMAX];
long long ans;
deque<int>d;
int main()
{
    f>>n>>k;
    for(int i=1;i<=n;i++)
        f>>v[i];
    for(int i=1; i<=n; i++)
    {
        while(!d.empty() && v[i]<=v[d.back()])
            d.pop_back();
        d.push_back(i);
        if(d.front()==i-k)
            d.pop_front();
        if(i>=k)
            ans+=v[d.front()];
    }
    g<<ans;
    return 0;
}