#include <bits/stdc++.h>
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");


deque < int  > deq;
int v[5000006];



int main()
{
    long long n;
    in>>n;
    long long k;
    in>>k;
    long long s=0;
    for(int i=1;i<=n;i++)
    {
        in>>v[i];
    }
    for(int i=1;i<=n;i++)
    {
        while(!deq.empty() and v[i]<v[deq.back()])deq.pop_back();
        if( !deq.empty() and deq.front()==i-k )deq.pop_front();
        deq.push_back(i);
        if(i>=k)s+=v[deq.front()];
    }
    out<<s;

    in.close();
    out.close();
    return 0;
}