#include <iostream>
#include <fstream>
#include <deque>

using namespace std;

long long n,k,a[5000010];
deque<long long>d;

void citire()
{
    ifstream fin("deque.in");
    fin>>n>>k;
    for(long long i=0;i<n;++i)
        fin>>a[i];
}

void fctdeque()
{
    long long suma=0;
    d.push_back(0);
    for(long long i=1;i<n;++i)
    {
        if(!d.empty())
            while(a[d.back()]>=a[i])
            {
                d.pop_back();
                if(d.empty())
                    break;
            }
        d.push_back(i);
        if(i>=k-1&&!d.empty())
        {
            if(d.back()-d.front()>=k)
                d.pop_front();
            suma+=a[d.front()];
        }
    }
    ofstream fout("deque.out");
    fout<<suma;
}

int main()
{
    citire();
    fctdeque();
    return 0;
}