#include <bits/stdc++.h>
using namespace std;

ifstream in("deque.in");
ofstream out("deque.out");
const int N=5e6+5;
int v[N];

int main()
{
    int n,k;
    in>>n>>k;

    deque<int> dq;
    long long s=0;
    for(int i=1;i<=n;i++)
    {
        in>>v[i];
        while(!dq.empty() && a[i] <= a[dq.back()]) dq.pop_back();
        dq.push_back(i);

        if(dq.front() == i-k) dq.pop_front();
        if(i>=k) s+=v[dq.front()];
    }
    out<<s;
    return 0;
}