#include <bits/stdc++.h>

using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");

int n,k,a[5000001];
long long s;
deque<int> x;

int main()
{
    f>>n>>k;
    for(int i=1; i<=n; ++i)f>>a[i];
    for(int i=1; i<=n; ++i)
    {
        while(!x.empty()&&a[i] <= a[x.back()])x.pop_back();
        x.push_back(i);
        if(x.front()==i-k)x.pop_front();
        if(i>=k)s+=a[x.front()];
    }
    g<<s;
    return 0;
}