#include <iostream>
#include <fstream>
#include <deque>
using namespace std;

int N, K;
deque<pair<int, int> > G;

int main() {
    fstream f1, f2;
    int i, j, S=0;
    f1.open("deque.in", ios::in);
    f1>>N>>K;
    for(i=1; i<=K; i++) {
         f1>>j;
         while(!G.empty() && j<=G.back().first) {
              G.pop_back();
         }
         G.push_back(make_pair(j, i));
    }
    S+=G.front().first;
    for(i=K+1; i<=N; i++) {
         f1>>j;
         while(!G.empty() && G.front().second<=i-K) {
              G.pop_front();
         }
         while(!G.empty() && j<=G.back().first) {
              G.pop_back();
         }
         G.push_back(make_pair(j, i));
         S+=G.front().first;
    }
    f2.open("deque.out", ios::out);
    f2<<S<<endl;
    f1.close(); f2.close();
    return 0;
}