#include<fstream>
#include<deque>
#include<algorithm>

using namespace std;

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

long long x,n,k,i,S;
deque<pair<int,int> > Q;

int main()
{
    in>>n>>k;
    for (i=1;i<=n;i++)
    {
        in>>x;
        while (Q.size() && x<Q.back().first)
            Q.pop_back();
        Q.push_back(make_pair(x,i));

        if (i>=k)
            S+=Q.front().first;

        if (i-Q.front().second+1==k)
            Q.pop_front();
    }
    out<<S;
}