#include <bits/stdc++.h>
#define maxn 5000010
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");

int sir[maxn];

int main() {
    int n, k, suma = 0;
    deque <int> coada;
    
    fin >> n >> k;
    for(int i = 1; i <= n; ++i)
         fin >> sir[i];
    
    coada.push_back(1);
    for(int i = 2; i <= n; ++i) {
        while(sir[i] <= sir[coada.back()])
              coada.pop_back();
        
        coada.push_back(i);
        
        if(coada.front() == i - k)
            coada.pop_front();
        
        if(i >= k)
           suma += sir[coada.front()];
    }
    fout << suma;
}