#include <iostream>
#include <fstream>
#include <deque>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
deque <int> a;
int v[5000005];
int main()
{
    int i,n,k;
    long long s=0;
    fin>>n>>k;

    for(i=1;i<=n;i++)
        fin>>v[i];
    a.push_back(1);
    for(i=2;i<=n;i++)
        {
            while(v[i]<v[a.back()]&&!a.empty())
                a.pop_back();
            a.push_back(i);
            if(a.front()<=i-k)
                a.pop_front();
            if(i>=k)
                s+=1LL*v[a.front()];
        }
    fout<<s<<'\n';
    return 0;
}