#include <bits/stdc++.h>
using namespace std;

int dq[5000006], a[5000006];
int main(void){
    ofstream cout("deque.out");
    ifstream cin("deque.in");
    int n, k;
    cin >> n >> k;
    for(int i = 1;i<=n;i++){
        cin >> a[i];
    }
    dq[1] = 1;
    long long int suma = 0;
    int st = 1, dr = 1;
    for(int i = 1;i<=n;i++){
        while(st <= dr && a[i] <= a[dq[dr]]){
            dr--;
        }
        dq[++dr] = i;
        if(i - dq[st] == k){
            st++;
        }
        if(i >= k){
            suma += a[dq[st]];
        }
    }
    cout << suma;

}