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