#include<iostream>
#include<fstream>
#include<deque>

using namespace std;

int main()
{
    int n, a[5000000],k;
    long long s = 0;
    deque<int>d;
    ifstream in;
    ofstream out;
    in.open("deque.in");
    out.open("deque.out");
    in>>n>>k;
    for(int i=0;i<n;i++)
    {
            in>>a[i];
            while(!d.empty()&& a[d.back()]>=a[i])
                d.pop_back();
            d.push_back(i);
            if(i-d.front()<k && i+1>=k)
                s+=a[d.front()];
            else if(i>=k)
            {
                d.pop_front();
                s+=a[d.front()];
            }
    }
    out<<s;
}