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

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

long long n,k,x,s;
deque<int> dq;
vector<int> v;
int main()
{
    fin>>n>>k;
    for(int i=1;i<=n;i++){
        fin>>x;
        v.push_back(x);
    }
    for(int i=0;i<n;i++){
        while(!dq.empty() and v[dq.back()]>=v[i])
            dq.pop_back();

        dq.push_back(i);
        if(i-dq.front()>=k)
            dq.pop_front();
        if(i>=k-1 and !dq.empty())
            s+=v[dq.front()];
    }
    fout<<s;
}
/*

9 3

-7 9 2 4 -1 5 6 7 1
 0 1 2 3  4 5 6 7 8
*/