#include <bits/stdc++.h>
using namespace std;
long long s;
int v[5000001];
deque <int> v2;
int main()
{
    ifstream fin("deque.in");
    ofstream fout("deque.out");
    int n,k;
    fin>>n>>k;
    for(int i=1;i<=n;i++)
    {
        fin>>v[i];
        while(!v2.empty() && v[i]<=v[v2.back()])
            v2.pop_back();
        v2.push_back(i);
        if(v2.front()==i-k)
            v2.pop_front();
        if(i>=k)
            s+=v[v2.front()];
    }
    fout<<s;
    return 0;
}