#include <bits/stdc++.h>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
const int Nmax=5000001;
int n, k, A[Nmax];
deque <int> d;
long long Sum;
int main()
{   f>>n>>k;
    for(int i=1;i<=n;i++) f>>A[i];
    for(int i=1;i<=n;i++)
    {   while(!d.empty() and A[i]<=A[d.back()]) d.pop_back();
        d.push_back(i);
        if(d.front()==i-k) d.pop_front();
        if(i>=k) Sum+=A[d.front()];
    }
    g<<Sum<<'\n'; g.close(); return 0;
}