#include <bits/stdc++.h>
#define ll long long int

using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
ll x,n,k,v[5000001],sum;
deque <ll> d;

int main()
{
    fin>>n>>k;
    for(ll i=1;i<=n;i++)
        fin>>v[i];
    for(ll i=1;i<=n;i++)
    {
        while(!d.empty()&&v[i]<=v[d.back()])
            d.pop_back();
        d.push_back(i);
        if(d.front()==i-k)
            d.pop_front();
        if(i>=k)sum+=v[d.front()];
    }
    fout<<sum;
}