#include <iostream>
#include <algorithm>
#include <fstream>
#include <vector>
#include <deque>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
vector<int> result;
int n,k,x;
int a[5000001];
long long sum=0;
deque<int> de;

int main()
{
    fin>>n>>k;
    for(int i=0; i<n; ++i)
        fin>>a[i];
    for(int i=0; i<k; ++i)
    {
        while(!de.empty()&&a[i]<a[de.back()])
            de.pop_back();
        de.push_back(i);
    }
    result.push_back(a[de.front()]);
    if(de.front()==0) de.pop_front();
    for(int i=k; i<n; ++i)
    {
        while(!de.empty()&&a[i]<a[de.back()])
            de.pop_back();
        de.push_back(i);
        result.push_back(a[de.front()]);
        if(de.front()==i-k+1)
            de.pop_front();
    }
    for(int i=0; i<result.size(); i++)
        sum+=result[i];


    fout<<sum;

    return 0;
}