#include <fstream>
#include <deque>

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