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

int deq[5000005], a[5000005];
int main(void){
    ofstream cout("deque.out");
    ifstream cin("deque.in");
    int n, k;
    cin >> n >> k;
    int st = 1, dr = 0;
    long long int s = 0;
    for(int i = 1;i<=n;i++){
        cin >> a[i];
    }
    deq[1] = a[1];
    dr =1;
    for(int i = 1;i<=n;i++){
        while(st<=dr && a[i] <= a[deq[dr]]){
            dr--;
        }
        deq[++dr] = i;
        if(i - deq[st] == k){
            st++;
        }
        if(i >= k){
            s += a[deq[st]];
        }
    }
    cout << s;
}