#include <iostream>
#include <fstream>
#define N 5000001
using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");

int a[N], deque[N], first, last, n, k;
long long sum;

int main()
{
    fin >> n >> k;
    for(int i = 1; i <= n; i++)
        fin >> a[i];
    for(int i = 1; i <= n; i++)
    {
        while (first <= last && a[i] < a[deque[last]])
            last--;
        deque[++last] = i;
        if(deque[first] <= i - k)
            first++;
        if(i >= k) sum+= a[deque[first]];
    }
    fout << sum;
    return 0;
}