#include <bits/stdc++.h>
#define pii pair<int, int>

using namespace std;

int v[5000003];
deque <pii> dq;

int main()
{
    ifstream cin("deque.in");
    ofstream cout("deque.out");

    long long n, k, ans=0;
    cin>>n>>k;
    for(int i=1; i<=n; i++)
    {
        cin>>v[i];
    }
    for(int i=1; i<=n; i++)
    {
        while(!dq.empty() && dq.back().first>v[i])
        {
            dq.pop_back();
        }
        dq.push_back({v[i], i});

        while(!dq.empty() && dq.front().second<i-k+1)
            dq.pop_front();

        if(i>=k)
            ans+=dq.front().first;
    }
    cout<<ans;


    return 0;
}