#include <bits/stdc++.h>
#define pos first
#define val second
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
deque<pair<int,int>> q;
int n,k,x,y;
int64_t s;
int main()
{
    f>>n>>k;
    for(int i=1;i<k;i++)
    {
        f>>x;
        while(q.size()&&q.back().val>=x)q.pop_back();
        q.push_back(make_pair(i,x));
    }
    for(int i=k;i<=n;i++)
    {
        f>>x;
        while(q.size()&&q.back().val>=x)q.pop_back();
        q.push_back(make_pair(i,x));
        if(q.front().pos==i-k)q.pop_front();
        s+=q.front().val;
    }
    g<<s;
    return 0;
}