#include <bits/stdc++.h>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
long long i,n,v[5000005],k,S;
deque<int>q;
int main()
{
    f>>n >>k;
    for(i=1;i<=n;i++)f>>v[i];
    for(i=1;i<=k;i++)
    {
        while(!q.empty() && v[q.back()]>=v[i])q.pop_back();
        q.push_back(i);
        if(i-k==q.front())q.pop_front();
    }
    S+=v[q.front()];
    for(i=k+1;i<=n;i++)
    {
        while(!q.empty() && v[q.back()]>=v[i])q.pop_back();
        q.push_back(i);
        if(i-k==q.front())q.pop_front();
        S+=v[q.front()];
    }
    g<<S;

}