#include <fstream>
#include <deque>

using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");


deque<int> dq;
long long sum;
int a[5000001],n,k,i;

int main()
{
    cin>>n>>k;
    for(i=1; i<=n; i++)
        cin>>a[i];
    for(i=1; i<=k; i++)
    {
        while(!dq.empty()&&a[dq.back()]>=a[i])
            dq.pop_back();
        dq.push_back(i);

    }
    sum=a[dq.front()];

    for(i=k+1; i<=n; i++)
    {
        if(dq.front()<i-k+1)
            dq.pop_front();
            while(!dq.empty()&&a[dq.back()]>=a[i])
                dq.pop_back();
        dq.push_back(i);
        sum+=a[dq.front()];
    }
    cout<<sum;
    return 0;
}