#include <bits/stdc++.h>

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

int64_t s,n,k,v[5000005];
deque <int> Q;
int main()
{
    f>>n>>k;
    for(int i=1; i<=n; i++)
        f>>v[i];
    for(int i=1; i<=n; i++)
    {
        while(!Q.empty()&&v[i]<=v[Q[Q.size()-1]])
        Q.pop_back();
        Q.push_back(i);
        if(Q.front()==i-k)Q.pop_front();
        if(i>=k)s+=v[Q.front()];
    }
    g<<s;
    return 0;
}