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