#include <fstream>
#include <algorithm>
#include <cmath>
#include <deque>
using namespace std;
deque <int> v;
long long sum;
int a[5000001],i,n,k;
int main()
{
    ifstream f("deque.in");
    ofstream g("deque.out");
    f>>n>>k;
    for (i=1; i<=n; i++)
    { f>>a[i];
        while (!v.empty() && a[v.back()]>=a[i]) v.pop_back();
        v.push_back(i);
        if (v.front()<=i-k) v.pop_front();
        if (i>=k) sum=sum+a[v.front()];
    }
    g<<sum;
    f.close();
    g.close();
    return 0;
}