#include<iostream>
#include<fstream>
#include<deque>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
deque<pair<long long, long long> >my_deq;
long long n, k, i, x, s=0;
int main()
{
    f>>n>>k;
    for(i=1;i<=n;i++)
    {
        f>>x;
        while(x<=my_deq.back().first && !my_deq.empty())
                my_deq.pop_back();
        my_deq.push_back(make_pair(x, i));
        if(my_deq.front().second == i-k)
            my_deq.pop_front();
        if(i>=k)
            s+=my_deq.front().first;
    }
    g<<s;
}