#include <bits/stdc++.h>

using namespace std;
ifstream fin("nrtri.in");
ofstream fout("nrtri.out");
int n,k,v[5000005];
int main()
{
    fin>>n>>k;
    for(int i=1;i<=n;i++)
        fin>>v[i];
    long long s=0;
    deque<int> dq;
    for(int i=1;i<=n;i++)
    {
        while(!dq.empty()&&v[i]<=v[dq.back()])
            dq.pop_back();
        while(!dq.empty()&&dq.front()<=i-k)
            dq.pop_front();
        dq.push_back(i);
        if(i>=k)
            s+=v[dq.front()];
    }
    fout<<s;
    return 0;
}