#include<bits/stdc++.h>

using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");

int n , k;
deque<int> dq;
int v[5000001];

int main(){
    fin >> n >> k;
    for(int i=  1 ; i <= n ; i++) fin >> v[i];
    for(int i = 1 ; i < k ; i++){
        while(!dq.empty() && v[i] <= v[dq.back()]) dq.pop_back();
        dq.push_back(i);
    }
    long long sum = 0;
    for(int i = k ; i <= n ; i++){
        while(!dq.empty() && v[i] <= v[dq.back()]) dq.pop_back();
        dq.push_back(i);
        while(i - dq.front() >= k) dq.pop_front();
        sum += v[dq.front()];
    }
    fout << sum;
}