#include <iostream>
#include <fstream>
#include <deque>
#define max1 5000010
using namespace std;
std::ifstream f("deque.in");
std::ofstream g("deque.out");

int n, k, v[max1], d[max1], a=1, b=0;
long long s=0;

int main()
{
    int i;
    f >> n >> k;
    for(i=1; i<=n; i++)
        f >> v[i];


    for(i=1; i<=n; i++)
    {
        while(a<=b && v[i] <= v[d[b]])
            b--;
        b++;
        d[b] = i;

        if(d[a] == i-k)
            a++;
        if(i>=k)
            s += v[d[a]];
    }

    g<<s;
}