#include <fstream>
#include <deque>

using namespace std;

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

long long n,k,i,x,sum,j;
int a[5000020];

deque < int > v;


int main()
{
    f>>n>>k;
    for(i=1;i<=k;i++)
    {
        f>>a[i];
        while(!v.empty()&&a[v.back()]>=a[i])
            v.pop_back();
        v.push_back(i);
    }
    sum+=a[v.front()];
    for(i=k+1;i<=n;i++)
    {
        f>>a[i];
        while(!v.empty()&& a[v.back()]>=a[i]  )
            v.pop_back();
        while(!v.empty()&& v.front()<=i-k)
            v.pop_front();
        v.push_back(i);

        sum+=a[v.front()];
    }
    g<<sum;
}