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

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

deque<int> D;
int n, k;
int a[5000000];

void addToDeque(int x)
{
    while(!D.empty() && a[D.back()] > a[x])
    {
        D.pop_back();
    }
    D.push_back(x);
}

void solve()
{
    long long sum = 0;
    f>>n>>k;
    for(int i = 0; i<n; i++)
    {
        f>>a[i];
        if(i >= k)
        {
            if(D.front() == i-k)
                D.pop_front();
        }
        addToDeque(i);
        if(i >= k-1)
        sum += a[D.front()];
    }
    g<<sum;
}

int main()
{
    solve();
    return 0;
}