#include <bits/stdc++.h>
#define fr(i,n) for(int i=0;i<n;i++)
using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");

int n,v[5000001],k;

deque<int> q;

int main()
{
    f>>n>>k;
    int s=0;
    fr(i,n)
    {
        f>>v[i];
        if(!q.empty()&&q.front()==i-k) q.pop_front();
        while(!q.empty()&&v[q.back()]>v[i]) q.pop_back();
        q.push_back(i);
        if(i>=k-1)s+=v[q.front()];
        //g<<s<<'\n';
    }
    g<<s;
    return 0;
}