#include <bits/stdc++.h>
using namespace std;
long long N,K,a[5000005];
deque <long long> q;
int main()
{
    long long i,s=0,b=0;
    ifstream in("deque.in");
    ofstream out("deque.out");
    in>>N>>K;
    for (i=1;i<=N;i++)
    {
        in>>a[i];
        b=1;
        while (b)
        {
            if (!q.empty())
            {
                if (a[i]<=a[q.back()])
                q.pop_back();
                else
                    b=0;
            }
            else
                b=0;

        }
        q.push_back(i);

        if (i-q.front()>=K)
            q.pop_front();
        if (i>=K)
        s+=a[q.front()];
    }
    out<<s<<"\n";
}