#include <bits/stdc++.h>

using namespace std;
ifstream fin ("deque.in");
ofstream fout ("deque.out");
long long n, k, sum;
int a[5000005];
deque <int> dq;

signed main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    fin >> n >> k;
    for(int i = 1; i <= n; i++){
        fin >> a[i];
        if(i > k && dq.back() == i - k){
            dq.pop_back();
        }
        while(!dq.empty() && a[i] < a[dq.front()]){
            dq.pop_front();
        }
        dq.push_front(i);
        if(i >= k) sum += a[dq.back()];
    }
    fout << sum;
    return 0;
}