#include <bits/stdc++.h>

using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");

#define cin fin
#define cout fout

int n,k,i,a,s;

struct numar
{
    int val,poz;
};
numar x;

int main()
{
    cin>>n>>k;
    deque<numar> d;
    for(i=1;i<=n;i++)
    {
        cin>>a;
        while(!d.empty() && d.front().poz<i-k+1)
             d.pop_front();
        while(!d.empty() && d.back().val>a)
            d.pop_back();
        x.val=a;
        x.poz=i;
        d.push_back(x);
        if(i>=k) s+=d.front().val;
    }
    cout<<s;
    return 0;
}