#include <bits/stdc++.h>
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
int v[5000005];
int c[5000005];
int main()
{
    int n, k;
    in >> n >> k;
    int st = 0, dr = -1;
    int sum = 0;
    for(int i = 0; i < n; i++)
    {
        in >> v[i];
        if(c[st] == i - k)
            st++;
        while(st <= dr && v[i] <= v[c[dr]])
            dr--;
        c[++dr] = i;
        if(i >= k - 1)
            sum += v[c[st]];
    }
    out << sum;
    return 0;
}