#include <bits/stdc++.h>

using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");

#define Nmax 5000010
deque <int> q;
int n,k,minn,s,v[Nmax];

int main()
{
    in>>n>>k;
    for(int i=1;i<=n;i++){
        in>>v[i];
    }
    for(int i=1;i<=n;i++){

     while(!q.empty() && v[i] < v[q.back()])q.pop_back();
     q.push_back(i);
     if(q.front() == i-k)q.pop_front();
     if(i >= k) s+=v[q.front()];
    }
    out<<s;

    return 0;
}