#include <fstream>
#include <deque>
#define pii pair<int,int>
using namespace std;
const int maxn=1e5+1;
int v[maxn];
ifstream cin("deque.in");
ofstream cout("deque.out");
deque<pii> mini;
int main()
{
    int n,k;
    cin>>n>>k;
    for(int i=0;i<n;i++){
        cin>>v[i];
    }
    for(int i=0;i<k;i++){
        int a=v[i];
        while(mini.empty()==false && a<mini.back().first){
            mini.pop_back();
        }
        mini.push_back({a,i});
    }
    int rsp=0;
    rsp=rsp+mini.front().first;
    //cout<<mini.front().first<<" ";
    for(int i=k;i<n;i++){
        int a=v[i];
        while(mini.empty()==false && mini.front().second<=(i-k))mini.pop_front();
        while(mini.empty()==false && a<mini.back().first){
            mini.pop_front();
        }
        mini.push_back({a,i});
        //cout<<mini.front().first<<" ";
        rsp=rsp+mini.front().first;
    }
    cout<<rsp;
    return 0;
}