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

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

int n,k, v[5000001], deq[5000001], start,END, i;
long long s;
int main()
{
    END = -1;

    f>>n>>k;

    for(i=0;i<n;i++)
        f>>v[i];

    for(i=0;i<n;i++)
    {
        while(start < END && v[i] <= v[deq[END]])
            END--;
        deq[++END] = i;
        if(deq[start] == i -k)
            start++;
        if(i+1 >= k)
            s += v[deq[start]];
    }
    g<<s;
    return 0;
}