#include <iostream>
#include <bits/stdc++.h>

using namespace std;
ifstream r("deque.in");
ofstream w("deque.out");
deque<int>d;
int v[5000002];
int main()
{
    int n, k;
    long long sum=0;
    r>>n>>k;
    for(int i=0; i<n; i++)
    {
        r>>v[i];
        while(d.size()!=0 && v[i]<d.back())
        {
            d.pop_back();
        }
        d.push_back(v[i]);
        if(i>=k-1)
        {
            if(i>=k && v[i-k]==d.front())
            {
                d.pop_front();
            }
            sum+=d.front();
        }
    }
    w<<sum;
    return 0;
}