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

using namespace std;

int main()
{   int n,i,s,k,a[500000];
    deque <int> d;

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

    f>>n;f>>k;s=0;

    for(i=1;i<=n;i++)
        {
            f>>a[i];
            while (!d.empty()&&d.back()>a[i]) d.pop_back();
            d.push_back(a[i]);
            if (i>k&&d.front()==a[i-k]) d.pop_front();
            if (i>=k)s=s+d.front();
        }

    g<<s;
    return 0;
}