#include <iostream>
#include <fstream>
#include <deque>
using namespace std;

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

int n, k, el;
long long sum;
deque <pair <int, int> > dq;

int main()
{
    f >> n >> k;
    for(int i = 1; i <= n; ++i) {
       f >> el;
       while(dq.size() && el <= dq.back().second)
            dq.pop_back();
       dq.push_back({i, el});
       if(dq.front().first < i - k + 1)
            dq.pop_front();
       if(i >= k)
            sum += dq.front().second;
    }
    g << sum;
}