#include<iostream>
#include<cstdio>
#include<deque>
using namespace std;
struct elem
{
    long long val, poz;
};
deque<elem>d;
elem aux;
long long n,k,s,i,x;
int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    cin>>n>>k;
    cin>>x;
    aux.val=x;
    aux.poz=1;
    d.push_back(aux);
    for(i=2; i<=k; i++)
    {
        cin>>x;
        while(d.empty()==false && x<d.back().val) d.pop_back();
        aux.val=x;
        aux.poz=i;
        d.push_back(aux);
    }
    s+=d.front().val;
    for(i=k+1; i<=n; i++)
    {
        if(d.front().poz<=i-k) d.pop_front();
        cin>>x;
        while(d.empty()==false && x<d.back().val)  d.pop_back();
        aux.val=x;
        aux.poz=i;
        d.push_back(aux);
        s+=d.front().val;
    }
    cout<<s;
    return 0;
}