#include <iostream>
#include <fstream>
#include <deque>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
deque <int> Dq;
int n,k,x,v[5000005];
long long s=0;
int main()
{
    f>>n>>k;
    for(int i=1;i<=n;i++)
        f>>v[i];
    Dq.push_back(1);
    for(int i=2;i<=k-1;i++)
    {
        while(Dq.size() && v[Dq.back()]>=v[i])
            Dq.pop_back();
        Dq.push_back(i);
    }
    for(int i=k;i<=n;i++)
    {
        while(Dq.size() && v[Dq.back()]>=v[i])
            Dq.pop_back();
        Dq.push_back(i);
        if(i-k==Dq.front())
            Dq.pop_front();
        s+=v[Dq.front()];
    }
    g<<s;
    return 0;
}