#include <fstream>
#include <deque>
#define NMAX 5000005

using namespace std;

ifstream cin("deque.in");
ofstream cout("deque.out");

int n,v[NMAX],k;
long long s;
int main()
{
    deque<int> deq;
    cin >> n >> k;
    for(int i=1; i <= n; i++)
        cin >> v[i];
    for(int i=1; i <= n; i++)
    {
        while(!deq.empty() and v[i] <= v[deq.back()])
            deq.pop_back();
        deq.push_back(i);
        if(i-k == deq.front())
            deq.pop_front();
        if(i >= k)
            s+=1LL*deq.front();
    }
    cout << s;
    return 0;
}