#include <bits/stdc++.h>

using namespace std;

deque< int > deq;
long long n,k,s,x;
vector< int >v;

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

int main()
{
    f>>n>>k;
    for(int i=1;i<=n;i++)
    {
        f>>x;
        v.push_back(x);
    }

    for(int i=0;i<k-1;i++)
    {
        while(!deq.empty()&&v[deq.back()]>v[i])
            deq.pop_back();
        deq.push_back(i);
    }
    for(int i=k-1;i<v.size();i++)
    {
        if(i-deq.front()==k)
            deq.pop_front();

        while(!deq.empty()&&v[deq.back()]>v[i])
            deq.pop_back();
        deq.push_back(i);

        s+=v[deq.front()];
    }
    g<<s;
}