#include<fstream>
#include<set>
#define x first
#define y second
#include<deque>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
deque<pair<int,int> >d;
int n,k,a;
long long r;
int main()
{
    fin>>n>>k;
    for(int i=1;i<=n;i++)
    {
        fin>>a;
        if(i!=1)
            if(d.size())
                while(d.back().x>=a)
                    d.pop_back();
        d.push_back({a,i});
        if(d.front().y<=i-k)
            d.pop_front();
        if(i>=k)
            r+=d.front().x;
    }
    fout<<r;
}