#include <bits/stdc++.h>

using namespace std;

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

const long long NMax = 5000005;

int main()
{
    long long n, k, sum = 0, val;
    fin >> n >> k;
    deque<pair<long long, long long>> dq;
    for(long long i=1; i<=n; ++i){
        if(!dq.empty()){
            if(dq.front().first == i - k){
                dq.pop_front();
            }
        }
        fin >> val;
        while(!dq.empty() && dq.back().second > val){
            dq.pop_back();
        }
        dq.emplace_back(i, val);
        if(i >= k){
            sum += dq.front().second;
        }
    }
    fout << sum << '\n';
    return 0;
}