#include <bits/stdc++.h>

using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
const int N = 5000010;
int n,k,a[N];
deque<int> q;
int64_t sol;
int main()
{
    f>>n>>k;
    for(int i=1;i<=n;i++)
        f>>a[i];
    for(int i=1;i<k;i++)
    {
        while(q.size()&&a[i]<=a[q.back()])
            q.pop_back();
        q.push_back(i);
    }
    for(int i=k;i<=n;i++)
    {
        while(q.size()&&a[i]<=a[q.back()])
            q.pop_back();
        q.push_back(i);
        if(i-q.front()==k)
            q.pop_front();
        sol+=a[q.front()];
    }
    g<<sol;
    return 0;
}