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

long long n, k, v[5000000], max1=5000000, d[5000000], a=1, b=0, s=0;

int main()
{
    long long 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;
}